Wow! I can't believe how many interpretations of this have come of this hijacked topic. Forget about when to shift, what is important is after you shift. The Spyder SE clutch isn't fully engaged until 3,200 rpm +/- 200 rpm. After you shift your rpm should not be lower than that if you are on the throttle. Higher rpm would actually be adviseable...you don't want to cut it too close.
My advice...when you are going down the road, try to remain at 4K or above. If you are cruising easy, on flat ground, at low throttle settings you may even get by with slightly less, but under no circumstance should an SE be operated below 3,500 rpm unless you want to risk clutch wear and eventual damage. You won't hurt this thing by keeping the rpm up, and you won't get better mileage by keeping it very low. The engine and clutch need to stay happy. They last longer and perform better if they are.
Thanks for that Scotty, I was about to try and re-summerize it myself.
One thing to note, and I know this will just add to the confusion of some:
Once above 3200+/-200 rpm (I would just say 3750 for safety buffer) the clutches lock up and won't unlock even if you go below that rpm until you get down to very low speeds in 1st gear to come to a stop.
Good:
From a stop, accelerate to 5200rpms, shift, watch the rpms drop to a very comfortable 4200rpms and continue to accelerate slowly and smoothly.
Bad:
From a stop, accelerate to 4000rpms, shift, watch the rpms drop to a clutch destroying 3000rpms, melt away ablative material until your rpms are above 3500 when the clutches finally can grab fully, assuming they're not damaged in which case it'll be 3600, or 3800, or 4200... or... time for a new transmission.
Not recommended but not bad for your clutches:
Accelerate to 5200rpms, shift, watch rpms drop to 4200... see the guy in front slow down, roll off the throttle and let the rpms drop to 3000... the clutches stay locked and no damage done. You can then, slowly, accelerate back up into the operating range of the Spyder. The problem with this is if you get on the throttle too hard, you lug the Rotax something fierce. More blowby, hard wear on the lower end, damage to ring lands... seriously cuts into the life of the engine.
I verified this with 2 BRP techs and 1 certified BRP technician. They all said the same thing. Keep it above 4000. Just... keep it there. Forget what gear or speed or what your neighbors think, just keep it above 4000... always. No reason to use it below those rpms, it's not designed to spend much time there.