I am hearing all types of stuff about this new Tahiti XT2 Chip for the upcoming release of the HD 7970 Ghz Edition, basically a HD 7975 coming out soon with a lower voltage and 175 mhz faster stock clock. It is supposed to be out by late June or early July. It is also supposed to be less money!! It may be a reallly good solution. For me, I have been waiting for the better GTX 680 Classified chips to be released the MSI Lightning GTX 680 or the HD 7970 GHz edition. I am curious about performance. http://www.techpowerup.com/167711/AMD-Radeon-HD-7970-GHz-Edition-quot-Tahiti-XT2-quot-Detailed.html
I would stick with the GTX 670. I initially went for the HD 7970's and had it clocked at about 1150 MHz. Everything was good, but I could no longer put up with the inductor buzzing, so I returned it and went for a GTX 670 DC2T. I get more FPS in BF3 with the GTX 670 than I did with my HD 7970. I understand this is just 1 game, but my point is that there is not a significant difference between GTX 670 and HD 7970. In short, stick with your Asus GTX 670. It has similar performance to the HD 7970, no inductor buzzing, better cooling, and it is quieter.
Don't think it'll be cheaper, but if you can wait, you might as well see how it turns out before deciding, this can be a serious overclocker. Just realised you have a 670.. There really would be no point in swapping imo. If you want more performance, go SLI.