Anything above 85c under full load is worrying. 50c is great.
If above 85c make sure you've not overclocked it, if it's still like that on default settings then remove heatsink remove dust, clean the surface of the GPU and the surface of the heatsink with isopropyl alcohol on a swab. Re-apply thermal paste, Arctic Silver 5, Arctic Cooling MX-4/MX-2, Cooler Master High Performance etc...
Still like that? Make sure you have good airflow in the case, google case airflow for some cool tips.
Still? :conf: Upgrade your heatsink with an aftermarket one. Arctic cooling do some amazing ones.
:ps: 350w PSU is criminally stupid. I wouldn't use any PSU less than 500w in any system I build.
Upgrade your PSU, cable manage the cables well, you can cable manage almost any case (even cheap shitty ones) to make them look like this...
