Personally, if it's a stock HX35, and you were not going to tow heavy or at altitude I'd run either housing.
If you do plan to tow, carry heavy a fair bit, or run with weight at altitude, then you should at least use the 14 WG version. That will help keep you out of the high drive pressures, and excess EGT's for the most part. Since the HX35 is a bit better turbo, alot of guys run with the 16cm NW housing for temp reasons at WOT.
Bob.