7970 Overclock help

I just got a new gaming rig and this is the first time I've had a PC capable of OCing. I've done a good bit of research but I still have a few questions.

Let me start by listing my specs:
I7 3770k OCed @ 4.6 cooled with H100i
16GB Corsair Vengence 1888
Windows 8
ASRock Extreme 4 MoBo
MSI Radeon 7970

Alright so I've got my CPU to a stable OC. I can push it further but the increased temps don't seem worth it. I doubt I can tell a .1 or .2 mhz difference anyway. Now I'm OCing my video card. I'm using MSI Afterburner. I pushed it to the max and the card handled it fine. I wanted to push it further so unlocked the max limits in Afterburner. It can handle the benchmark programs fine but the game seem to be what is limiting how far I can OC. Tera Online actually seems to be the most fickle when it comes to OCing.

Right now the OC I'm using is 1.29v. The core clock is 1175mhz and my memory clock is 1800mhz. Now to the questions.

Is that amount of voltage ok for everyday use? My card idles in the low 50's at that voltage compared to the 30's at stock. Is this ok? At full load I reach temps in the high 70's and low 80's. This is only with 65% fan. Any higher than that and it's loud. I have it set to go to 100% if temps go over 85. Are temps in the low 80's ok or should I lower it?

When I push my core clock higher I start to get artifacts. It's different for each game. In Farcry 3 1175 is stable but in Tera I need to go down to 1150. I would like to hit 1200. Is there anyway I can acheive this? I've seen plenty of other cards that can. I know each card is different. Would more cooling get rid of artifacts? More voltage? (Even though I can't go any higher) Or did I hit my cards limits?

As to the memory clock I seem to be able to go higher than many people. I can push past 1800 in some games but again it's Tera that is limiting me. TBH I'm not sure what is better. Memory Clock or Core Clock?

Any advice on this OC or how I can improve or tweak it in anyway is welcome.