chip intake and exhaust tuning is from what I've read here, about all the stock transmission will handle (read in the ballpark of 300 horse here more than once)

there's plenty of other sources for many of the same things eastern offers (see volvotuning.com) usually with more realistic HP estimates...

I'd advise against boringout the 2.3, volvo shrunk the 2.4 to the 2.3 for reliability purposes. THe most cost effective upgrades are exhaust and chip tuning.

I suppose if money is no object whatsoever, you could put high-po lighter custom engine internals and balance and blueprint it... But that would easilly run in the $5,000+ range and the stock internals of the 2.3 are pretty close to exotic anyway, and with OBDII computers, you'd probably need a custom ECU to go with a performance rebuild.