As the topic says, what GTX 980 under 600 is the best (most overclockable). I was going to get the MSI with a badass custom backplate from V1Tech but I like what I have read about the G1. I am not waiting 3 plus months for the 300 series from AMD, if the 300 series is that good I will sell my 980 and get a 300 series card. I had 970's but returned them because of the 3.5 VRAM issue (even though my G1's were freaking awesome).
I've already done the crossfire 290x thing and I don't wan to do it again.
Why?
http://pcpartpicker.com/part/evga-video-card-04gp42983kr
I like the EVGA 980 acx 2.0 Superclocked. I hear good things about the acx cooler, and I feel that factory overclocked cards are easier to further overclock.
I have one of those, mine runs at 1392MHz out of the box. The cooler was very quiet, however it ended up back in the box because I decided to put a water block on it.
What games you running, and how is it performing?
Recently - Metro Redux, Crysis Series, Farcry 3 and Shadow of Mordor. Running at 1920x1080 constant 60 FPS maxed except no motion blur (I just don't like motion blur) or SSAA.
I would seriously consider an R9 295X2 if your are looking for performance. It should crush any GTX 980 in pretty much any AAA title.
But if you have to get a GTX 980 I would probably go Gigabyte G1 Gaming right now.