the stock bolt on the kwa mp7 will shoot 400 on a COLD day, if it's sunny and warm it will be over 400fps. I measured on a 25C day the mp7 was shooting 460fps in the sun.
The low power bolt assembly was shooting 365 in the same conditions.
I futz with V2s, V3s and V6s. I could be wrong... but probably, most likely not, as far as I know.