the GSR will kill the 240. don't buy into the hype - that thing has a truck engine(as stated above) and with the rw drive system that thing carries some massive weight.
my friend had a early 90's 240sx and i would destroy it in my 93 civic ex - we even switched cars to see if it was driving and he smoked me by near the same length. If I had my GSR I would have beat it by more.
Basically you can make them fast though and for cheap. my other car is a 95 G20 with a JDM (150hp) SR20DE motor in it - it gets smoked by my 'teg - but it pulls hard.