Mint FRST
EVERY 1.8t lump will be upto the job of 300bhp so conversion wise the best option is to buy a 150bhp motor and fit a bigger turbo cuse the only real difference between the ot of them are the mpping and the turbos as standard.
I'm doing a mk1 golf and wanting about 400bhp so bought a seat cupra 150bhp motor, the reason being is that i will be replacing the rods, pistons, turbo, and possibly a bit of head work so there was no point buying a 225 motor cause i'm replacing everything anyway.
Ps Chip i've never heard any differences between the valves just the ports in the head, plus if there was any difference it would be minimal imo