I would think hi 50"s. My old 400 did about 50, and my 700 does about 65. They can both get a bit scary at that speed but I do it once or twice a ride. ( just to blow out the carbon lol)

 

2nd

 

Saw 61 on my speedo (2011 Grizzly 550) on the road last year at H-M...fast enough for me!!

 

Saw 68-69 a few times down a steep paved hill on my 660. I wanted more. GPS for that very thing read 64-65. In its best day, it wouldn't get over 64 on a GPS on flat pavement wound out. Ran 59-60 on the GPS with 27" tires. Others that I ran a GPS with were a 99 Arctic Cat 500 topping out at 53-54, a 98 Arctic Cat 454 topping out at 52-53, and yes, a 1989 Fourtrax 300 2wd that somehow after a long wide open flat paved stretch eaked out 50-51 on the GPS once (and I know that doesn't sound likely, but take it or leave it). So definitely that 550 is going go faster than 50 on the top end.

 

700 grizzly supposedly does 63-67 MPH. I really don't care because I bought a "Utility" unit. Not that hitting the throttle here and there is not fun, but a "Sport" quad is maybe what should be used for ripping around. (Common sense).

All that said, ride to your ability. Stuff can happen quick, regret not.

Flathead

 

The March 2012 issue of Dirt Wheels did a Big Bore shoot out between 4 models . They tested the following all 2012 models and recorded these top speeds using a Trail Tech Voyager GPS unit.

Polaris 850 XP - 77 MPH Weight 830lbs
Can-Am Outlander 800 - 76 MPH Weight 880lbs
Brute Force 750 - 75 MPH Weight 695 lbs
Grizzly 700 - 70 MPH Weight 648lbs

The Grizzly won the shoot out as #1 machine