i own an excel with 2 1/4 inch zorst, Hve 4-1 extractors, Hve Tb, K&n filter and fueltronics chip. Its fast enuff to beat most STOCK commodores and falcons, all models up to EL for ford and Vt for commies, and most other similar 4's
BUT I would neva say its fast. I have to thrash the shit outta it to get it movin and consequently have done 2 boxes and a clutch cos of it.
Back to the topic of sleeper excels, the only reason i would go crazy moddin one is cos of power to weight, as i beleive excels weigh in at around 800-900 kg, so there pretty light.