I have exactly same pc and imho you should not have problem with x264 720p30 in OV but only if you fill these conditions
1. 60 desktop refresh
2. 30 in obs
3. 60 in game if there is switch for it (like bf3 or bf4)
4. vsync in game on
(replace with 59,94 and 29,97 for 59,94 display like hdmi tv)
with 144hz monitor its fastest and most reliable to sacrifice 144 and follow 1,2,3,4
ps. oc this cpu to 4.5 or 4.6 (mine works at 4.6)
http://www.overclock.net/t/1570313/skylake-overclocking-guide-with-statistics
if you cant/dont want to oc, you can still use quicksync
https://obsproject.com/forum/resources/how-to-use-quicksync.82/
https://obsproject.com/forum/resources/custom-parameters-of-quicksync.104/