Bris - I know this isnt really related to cam gears, and it costs money.
But have you thought about pulling the head off and having the ports tickled?
Wouldnt need much, and I wouldn't go any larger in port volume, but I have no doubt there are REAL gains to be had with a bit of a grind, espesially on the exhaust side of the 20 Head.
I would leave the standard cams as you are making power right through to the rev-cut, so unless you want another 1000rpm on top (which the 20g won't allow) I would definately leave the standard bump sticks, and as you found the the Apexi (I think) cams you went backwards.
If you do want cams + more mid range, have a look at getting some custom cams ground, with a smidge more lift and LESS duration than standard.
Anyhoo, hope you get it sorted
Andrew
Quick Edit -
Bris, That little RB20 is making something like 210-220hp/L
Pretty good when you think of it like that.