120 is pretty optimistic without mods, I'd say like 110-112 without mods and 116-118 as turk says with some tweaking. I assume by this he means the "usual stuff" reednotch/reedspacers, thinner headgasket and silencer bore.
The power valve motors are great for exelleration and speed. The SRX is made low to the ground for better control at hight speeds. It is known as a lake racer and one of the best out there for that at about 138hp stock.
The SXR is a long travel trail sled. Comfortable and real smooth in the trails.
they are on average about 112hp stock.
Nothing about the motors are the same and alot of guys that like the speed of the SRX are making them long travel like the SXR.