benefits, faster acceleration, better drive out of corners. downside is less speed achievable in each gear. top speed limited to about 260-280 depending on rev limit.
the parts themeselves are not too expensive (but a bit tricky to find) but there is a fair bit of work in fitting them. for the front you basically need to remove the engine, then remove the sump. rear is obviously drop the cradle and remove the diff. just remember if you do it you will need the front crown wheel and pinion and the shaft it's on, and the rear crown wheel and pinion too.