RB20s are crap off boost. think of it like this, a 2 litre towing a 1300kg car, slow... 235rwkw from a 20 makes me think it would be really laggy which would then make the painful wait for boost even longer! i know mine is painful but my boost starts at just over 2000rpm (stock turbo lol)
having said that i don't know what difference cams and some of the other mods would make, mine only makes just over 160rwkw