xps is a bit too overconfigured for its dimensions. There have been reports of GPUs on XPS 15 and 16 frying off after an year or so of heavy gaming.

so in case you insist on XPS then make sure you get 3-yr extended warranty for it as well.

the 17" will remain cool and extended warranty need not be required on that. Ofcourse you compromise slightly on portability.

if you don't intend to lug your rig everyday, then the 17" would be a better choice for gaming.