LOL, heres what i know about the 05 cr125-it needs a decent piston and ring-like a vertex or wiseco, the head doesnt seem bad design, im not sure you will get a v force for it yet?? the inlet looked different but ive not looked at a very recent cr for a while, in the past a v force helped but didnt add that much, on the 03 i think it lost power(steve will remind me)
the exhuast port needs to be raised and also the jetting was rich on the one i tested.A pipe helped the 04 a little.
So i would say a pipe, jetting and maybe porting.