Well... My N/A isn't slow
But i see what your getting at, NA skylines are not rocket ships but performance itself is subjective (for example an NA skyline feels quick compared to a charade).
Strickly going off my own experience and drag and drift events I've attended you can assume the following:
0-100 ~8 seconds
1/4 mile 15.8 manual 16.3 auto (assuming you can drive, and as such you can expect to get your doors blown off by a lot of things, this includes Any falcon or commodore after about 1995)
Modification wise as stated MANY times on these forums extractors 2.5 inch exhaust rear muffler and centre resonator leave the stock air box, coil overs, a nice set of rims, also due to there age even LSD equipped models (type s) will peg leg so if u can deal with that good if not well its not worth the fuss on a Natro (don't weld it as its more hassle then it's worth, and keep it clean for god sake!)
For drift days I wouldn't attempt this unless you have stiff as hell coilovers bald skinny tires and preferably a bit of liquid horsepower (rain).
TLDR
You'll lose to falcodores
Don't waste to much money
Yes they are relatively slow
Edit: info and experience based on Natro rb25s