You really cannot rely on what
OTHERS get from a tank of gas in their Spyders/riding, cos there's just
sooo many variables that can mean what they get might have absofreakinlutely
NOTHING in common with what you might get!! Your altitude; the ambient temperature; what gas you've used; how full you fill your tank; how hard you twist your wrist; your tire pressures; the road surfaces you're riding on; and a whole heap more can all make enough of a difference that if you rely on someone else's averages, instead of arriving 'safely' at your next refill spot, instead you end up with an 'out of gas' Spyder sitting by the side of the road, having started the destruction of your fuel pump!!
So 'about 30 mpg' is a reasonable measure to use as an initial comparison to work from, but anyone else's 'average gas milage on 1 tank of gas'
might not only be meaningless to you, it could also be downright dangerous to even try to match that, let alone rely on it to determine how far you can safely go!!
So, that said, where did you get 6.6 gallons from?? IIRC, that's the figure for the 2014 & on 1330 powered RT's and all of the F3's, which have a larger gas tank than the GS's, RS's, RSS's, ST's, & RT's up 'til 2013. Besides, I'm not up to recalling the exact content &/or the conversion between litres and real gallons atm, let alone trying to work out those funny gallons you lot use in North America, but the V-Twins all have about 22 litres in total swept volume gas tanks (including the expansion space above the filler) and of that, only 20 litres is really useable.
Regardless, if you're pushing to use more of the tank and plan on running it to empty, or even close to that, then
DON'T!! 
At least, not without working out what
YOU generally get in the way of MPG in
YOUR riding and staying within that range; not unless you want to risk destroying the fuel pump, the injector system, &/or maybe even the engine!! (and I'd suggest that you really don't pooh-pooh that, as I've just recently seen
yet another Spyder engine that's ended up needing a pretty comprehensive rebuild cos the owner ran the tank dry and damaged the fuel pump and injector system enough such that cos they didn't really understand why the engine was losing power, they kept on until they'd stuffed it too!!
)
Modern fuel injection systems, especially those with the pump in the gas tank like our Spyders, use the gas remaining in the tank as both coolant and lubricant for the fuel pump, the injectors, and the injection system, so they
REALLY NEED to keep an
absolute minimum of about 2 litres of gas in the tank or there's not enough gas left in there to do all the things being asked of it adequately - so aiming to keep a little bit more gas in there is better, cos we all know how often we tend to end up trying to stretch things out juuust a little bit further, but unless you've got the remaining capacity to cater for it, doing that and running the gas remaining level too low can cause all sorts of damage, even if you don't notice it immediately!! This sort of damage is initially microscopic, but once it's started, even just a
tiny bit, every rotation of the pump from there on in makes the damage a tiny bit worse, and over time, that all adds up, until eventually...
So until
YOU work out
YOUR average MPG, it's
probably OK to work on getting about 30 mpg from the around 5 useable gallons in the tank, but you really should do that ASAP! Then work out how far you can safely travel on however much gas you usually end up putting in at a refill, always allowing for that minimum level of gas remaining in the tank. My 2013 RT has had an ECU Upgrade, so I get about the same mpg as most std 1330 Spyders, up in the high 30's mpg, better if I can resist the temptation to use the extra power available at the twist of my wrist (cos doing so will show pretty much all 1330 powered Spyders a clean pair of heels, excepting maybe those with a similar ECU Upgrade, but it does use more gas!!
) But I still have the smaller gas tank, so even when I am getting the same sort of MPG, I
STILL need to refill about 40-50 miles (or sometimes more) sooner!
And btw, if you have a 2016
RSS with the V-Twin motor, then you've probably got an SM
5, and not an SM6 - the 6 speed gearboxes only came out with the 1330 motors, and they are only available in the 2014 and on RT's, and in the F3's.
The V-Twin motors with the 5 speed boxes juuust
LOVE revs, and while you can get away with changing up in an SM5 (manual) box before 3300 rpm or so, there's really no advantage - their power band really comes on song at about 4,000 rpm and peaks up around 8,000+ rpm, with quite a bit more to the red line, altho the Spyder versions of these engines have been restricted and detuned a fair bit too, so don't be afraid to use the revs. In other platforms, these same engines are safely and reliably capable of revving out well beyond 9000 rpm, as some of us who have had an ECU Upgrade to unleash some of that untapped power can happily attest, so
REALLY, don't be scared of using the revs - in fact, with the standard tune, you are more likely to damage things by
NOT revving them hard enough than you are by over-revving... the ECU won't let you rev too hard anyway!! Back in the early days, quite a few SE5 semi-auto's had operator caused clutch problems basically because the riders weren't revving them hard enough, and they destroyed their clutch!! However, on your SM5, for the best economy, you should probably aim to keep your revs between about 3500 & 5500 rpm - anything much lower is likely to be lugging the engine and won't be helpful to it &/or the clutch
OR your overall economy/range; anything much higher than that will definitely produce more power and a zippier ride, and could be helpful for economy too, but if you're aiming for the absolute best economy you can manage &/or the best possible range, that rev range should be pretty good!
Enjoy!
You went around that tree several times!
