oh wow!! you're right. Just checked ebay and 770m is like under $400. I just assumed all high-end nvidia chips would be crazy expensive like the 680m. Thanks alot for bringing this to my attention! The games I want to play are better with nvidia anyway. Are you sure my CPU won't bottleneck the 770M?

Question: Why is the 770 so much less than the 680? I would assume they have about the same performance, correct?

Asus bios is not cross compatible or should I say its not compatible even with same vendor

So are you saying that the G53SW bios is not compatible with any ATI chips? Even if you modded their vbios?

No 680m still scores around 2000 more Points in 3dmark11. But pricewise it costs double amount. Here is link to my score With 680m: http://www.3dmark.com/3dm11/7630058
I have both 2630qm and 2860qm but no noticable differnces in performance in games. So answer is no it wont bottleneck your g53.
As for bios compatibility it is hard to say. As I have tried only nvidia gpu's so far. Anyhow I know guys that tried other nvidia cards like 670m and 660m and got black screen with no post. So if nvidia cards not working I really dont expect that asus bother to implement support for ati/amd cards 🙂
And on end to say asus actually follow only its own way of implementing MXM standards so best starting point is to expect nothing and be happy if your screen atleast litt with no picture at all 🙂

Hope this helped you bit better understanding your possibilities.