Might add my input here because i have a GTS20 manual... the cars got a full exhaust, just been serviced, and has its timing advanced a fair bit (made a massive difference).
A mate from work has a VY series II s pack manual... and we can drive about the same.
I've ran him twice for argument sake, once before timing, and once after.
The first time i got creamed (6-7 car lengths) and i was running very poor, i then ran him again after timing, this time i was running fairly decent (still a bit cold but we both were) we raced twice off two different sets of lights, the first set was around a corner for take off and i got about 3 car lengths off the start but then he pulled it into about even after a few hundred meteres. The second set was on the straight but continued up a ramp which went around a corner, this one i had a car length off the start held it for a bit then he pulled it in and eventually pulled a length on me (over about 400m) but then once it came to the corner i ripped him badly (easy 10 lengths) because they just dont handle.
It was clear his car was faster in the straight, but not HEAPS faster, you could also tell that my car was definetly faster through the corners. Baring in mind i have a Rb20, not Rb25 and my car has an exhaust, lots more timing, also has brand new pedders suspension, including shocks, springs, and its got sway bars etc. + it had just been serviced, against a stock VY II s pack.
You should be looking for the over all package mate and what you can afford, not 'whats faster' because if its the corners you will be, but if its the straight you wont be. At the end of the day im happy with what ive got, and couldnt be any happier with it:)
Dayne