Maybe your VCT wasn't working because there is a difference. Considering i can control my VCT with the microtech and turn it on or off, yep, there is a difference. Good mate of mine took the VCT off of his S15 because they tend to fail on the SR20 and he regrets it, very noticable power loss down low.
I'd be curious to see how a stock turbo RB26 would go with VCT on it considering i find them quite crap down low for what they are, however that's probably just lag from the twin setup (maybe this aint as bad on a R34, only been in R32 and R33 GTR's).