The PSE will give you a glorious sound, but no increase in power. The genuine PSE shot up in price recently, and the parts alone now cost £3400. If you don't need a switchable system (ie you don't do track days, or you have a Porsche warranty) then there are plenty of aftermarket systems for around £600 which will give a similar sound.
The 996 Carrera n/a engine is well mapped in the first place, and there aren't huge gains to be made in a remap. The best you can expect is probably 20bhp, so not much in terms of percentage, especially on your X50 engine which has a different map to the standard 996 anyway. If you do decide to go for it, choose a trusted and experienced outfit. There are plenty of cowboys around.
Personally, I'm not a fan of the K&N filter. IMO 23bhp increase is a wildly optimistic claim, to say the least. Also, if the filter is over-oiled even a small amount it will fry a £300 MAF sensor in an instant. Do a search on RennList or RennTech, and you will see some pretty negative feedback. They do make a nice sound, but I would go for something like the Schnell cold air intake, which retains the original filter and gives an improved sound at a fraction of the cost.
Just my 2p's worth.