After see'ing both run stock, i dont believe the traxxas stats. I think they are abit hyped, probably as part as thier advertising. I think the 2.5 and the CV-R are very comparable in power. With the OS being alot more reliable and alot less temperamental
I put a CV-R(x) 15 in mine awhile back. has alot more compression than my buddies freshly rebuilt 2.5 . I had no real problems keeping up besides running way rich because the OS head sucked. If you get the OS, Buy the Crazy Nut head. Well worth the $55 shipped. He already had a CRAZY nut head running lean on his. Waiting for my head to get here. Now i can show that 2.5 who the real boss is
Also i stuck with the rotory carb, it seems to have alot more mid range control. Rather than the Snappy on/off of the slide carb.
Get yourself a good pipe. The stock traxxas pipe seemed to suck with the OS. I just went with an AE torque Pipe. Have yet to run it. But thats what i was told to get for the OS motor from other OS drivers.
Oh yeah the CV-R(x) (short shaft) is a direct bolt in minus having to cut the shaft. You can use a die Grinder with a cut off disc. Or you can ask the hobby shop to do it for you in some cases.
I will post a pic of mine next week when i finish putting it together. Waiting for my new RPM arms.
Just my 2 cents.