true the whole point of a GTR is its potential, given it's age now a stock STI or Evo will at least keep up and probably surpass any stock R34 variant on the track. Put some mods in though and especially when you're wanting 400hp+ then the GTR does it far easier.
The different variants are worth it in my opinion. Even something as small as a standard GTR vs Vspec why bother saving $5k with a standard GTR when the vspec has better aero, LSD, attessa and engine sensors.