Originally Posted by Jordo!

Gains at peak don't necessarily tell you about gains under the rest of the curve.

I'd say best bang for the buck is K&N plus test pipes. Best gains for least cash. See my dynos below. You can find evidence of similar proportionate gains (tho' raw values may vary, as I've been saying) for others.

Whether or not those gains are worth it is subjective.

If you want really big power for relatively little cash, only other suggestion I have is nitrous.