Martin used to run standard boxes in his 500bhp Mondeo and Escort... some would last for a few months... but then others would last 10 yards... LITERALLY!

Its just a false economy. Especially if its a car you use often. You are driving a timebomb, it can go wrong at any time. Thats NO fun in my opinion. Don't forget unless you can change the box yourself, you have all the labour charges as well!

Diffs will be fine as long as you are not launching the life out of it. The front diff casing is the first thing to change when you have the funds.

P.S If your standard gearbox does last, you haven't got a real 500bhp either

Edit* Just read the bit about the antilag Yes that'll help! bring the 500bhp in lower and harder!