Alil upgrade work in the m4(prommy or Systema)

First of all ive been off doing stuff (football, school etc...) but im back.
The other day i was thinking about what I could do to maybe pump my m4 up alil, and i thought a mock suppresser and extended tb inner barrel, and a OD two tone paint job...It might lead to a full GB overhaul in the future, but im starting out small...
So I want to stick with the best of the best for internal upgrades (might as well do it big) and im torn between Prometheus and Systema, so i figured i'd ask which is better...
Prometheus http://www.airsoftpost.com/product_info.php?cPath=24_72_378&products_id=24388
or
Systema http://www.airsoftpost.com/product_info.php?cPath=24_72_380&products_id=24411

also what is the standard stock inner barrel length for an M4

PDI or Prometheus stainless 6.03 TBB are the best I have used by far. And the standard length for a M4 is 363mm

Systema's TBB are a hit or miss......i would go prommy or KM Head.

good deal...
prommy it is thanks guys