Some info i learned about the 2015 models.

Well first off is has been confirmed by people who test road them.
The 2015 RZR-S 900 is faster than a XP 900 , from 0 to 60 MPH
much better clutch and way better gearing is what they say.
even with less HP they say it has more torque than the XP 900.
The XP 900 is faster on top end by about 9MPH due to speed limiter on the ECU.
All 2015 RZRS have speed limiters built into the ECU.

All 2015 XP 1000 and RZR-S 900's have a top speed of 71 MPH
a 2014 XP 1000 will run 80 MPH. Yes people over at RZR.net are pissed..  
But the 2015 1000 will smoke a 2014 from 0 to 71 MPH. Thats confirmed as well.

Now the second shitty thing , All RZR's only run 15 MPH if your seat belt is not clicked.
but a simple fix is cut the 2 wires on the seat belt and jump them together , there already doing this....   
So you can add a harness.

As for the speed limiter , you take your ECU off your brand new 20,299 XP 1000 and 16,299 900-S and send it to some
guy on RZR . net and he re flashes it  and removes the speed limitor for $379 , and your new XP 1000 will top out at 86 MPH.

Honestly i dont really mind the speed limiter , Hell when do really need to go 85 MPH in an RZR....   
we never go much over 20 MPH in the woods anyway , and 71 MPH on the gravel road is flying in an RZR
900 or 1000....   

So there you have it. .....  

top speed is of no concern except to sand fleas and racers, totally unusable in the wood's