I can give you a review of the Zumo 665 but not a comparison as we've nvr had the 660
Lamont or anyone. Did you ever do a review on the 665 vs the 660?:dontknow:
The Garmin Zumo 665 was and is the very first GPS unit that I've ever had experience with, minus using the Nav app. on my Droid for the previous 2 years. The Droid actually worked very well, got Teddy & I all the way to Florida & back, to Cowtown once but died on our trip back from SpyderFest 2011. Since the phone wasn't water-proof I put it in a ziplock baggy with a rubber-band around it & that worked pretty well. On the trip back from SF'11, it was a heavy downpour & I thought I should be safe, and sealed the ziplock baggy:lecturef_smilie: causing heat & condensation to build up with no where to escape & killing the phone:shocked: Lesson learned

pps:Hence the purchase of the Zumo 665 that is weather resistant & made for MC travel.
At first, I hated it cause I didn't have the XM subsription with Nav Weather & Nav Traffic, just using the GPS by itself. The User Interface (pushing the buttons) isn't nearly as sensitive as my Droids, so that took some getting used to. I wish the overall size of the unit was a little larger, that way you could have larger keys to tap, all on one screen. You can increase key size, but then you have to go thru multiple pages of keys & that takes more time.
I have since added the XM subscription & really like the Nav Weather Alerts & the Nav Traffic Alerts as they work pretty well and are useful on daily rydes, when just cruising around, with no destination set, they will still alert you if there is Incliment Weather within like 50 miles of your current location or if the road/highway your currently ryding on has a traffic backup or delay, nice features but only with the XM subscription.
As for the XM music itself, I rarely use it, except for slow rydes. Not sure if I wired something incorrectly or what the reason is, but it seems the Volume when listening to XM music is about 1/2 that of all the rest of the audio output & at highway speeds, I can barely hear it.
And yes, I've double checked ALL of the audio output settings (on GPS & RT) to make sure they are ALL at MAX & they are. I'm pretty sure the 660 & 665 are the same machines with the 665 having the added XM capability & antanae disc included. Not sure if there are other differences or not. We mounted the antanae on the upper right hand side wind deflector that sits directly behind the windshield, and found that is a good out of the way place for it, and we DO get pretty good reception, minus the usual caveats of bridges, overpasses and tree covered roads.
Due to my volume issue with XM Music, we mostly use the MP3 feature of the 665 & listen to my tunes that way, no need to carry or store an Ipod with all my files on the 665, very convenient.
It also has a picture viewer & audio books source that you can upload onto & listen or view at your pleasure.
As with any GPS, the 665 is very customizable, from maps, display, routes, searches & even has blueTooth so you can pair it with you phone & headset & take & place calls directly from the 665 head unit, very convenient features.
I'm sure there's plenty more that I could write about, but if anyone has particular questions about the Zumo 665, feel free to ask.
We got ours over a year ago, caught it on sale from an internet retailer for under $700 & mounted it to the top dash using a $30 Ram mount, and ABSOLUTELY LOVE THAT POSITION, as it now acts as a Heads Up Display not only showing your route ahead, but also the speed limit along with your current speed, making looking at the RTs LCD screen almost unnecessary. And when we get to the twisties, I zoom the screen in for a very close view, and since its right in line of sight being on top of the dash, its almost like having a cheat-sheet of the twisties directly ahead, which one may not be able to see, so you have a couple of extra seconds to prepare, LOVE THAT!!!
In conclusion, its not cheap & its far from perfect, but IMHO, its worth every penny if you use it frequently. Most of the time now, I love just cruising with no destination programmed & with watching the display I've found SO many off beat roads that were Awesome, that I never would have taken, had I not had it, for fear of getting lost or running out of fuel.