Re: X50
It is very pricey for 30 HP more. But don't forget that it includes a modified exhaust system, new turbo chargers (K24 derivates), new intercoolers and a new gearbox (no oil cooler as on the GT2 though).
The 20 HP upgrade on the MY 2002 911 was part of a pretty "radical" facelift, even if it doesn't look that way at first look. BTW: most facelifted 996 run pretty good, achieving almost GT3 acceleration performance. No kidding.