I use Tekin RS Pro (haha, since your ID is Tekin708).
I tried Boost+10.5 vs NoBoost +8.5. Speed is about the same.
But, I like to use boost because I can fine tune the speed to match my friend's 1/12. With NoBoost+8.5, I have to change gearing, which I dont like doing at JV.
My friend is using SXXv2 + 4.5/4.0 and the ESC is very powerful too.
It depends on how many cell you will use.
1S:
SXXv2 is the best. since it is small and very powerful. It already has internal booster and Boost function. But lacking fine-tuning. ($12xx)
Hobbywing1S is also pretty good, costly only $8xx. It has booster and turbo functions, but just bigger.
2S:
Just keep your KO BMC. Its a nice ESC. With 6.6v + 7.5R, it is already quite fast la.