iMac Mid-2007 GPU Upgrade?

[iModFrenzy]

So I recently got a iMac Mid-2007 20", and it has a Radeon HD 2600 Pro in it(the original card).

I learned that the iMacs have upgradable cards and used a MXM slot. The 2600 isn't the best card so I was wondering what's the highest I can go upto?

Would a 8800GS be the highest?(I also heard these fail more, taking apart an iMac is not fun )

I saw a Mac HD 6750m GDDR5 512mb which uses MXM as well, would this card work in the iMac?

Thanks

 

[havokalien]

Not and have a boot screen or brightness control. May also have to modify the heat sink to fit the new card. For the cost of the card a newer used imac can almost be purchased.

 

[iModFrenzy]

Not and have a boot screen or brightness control. May also have to modify the heat sink to fit the new card. For the cost of the card a newer used imac can almost be purchased.

Ah okay, well boot screen is necessary to me/brightness. So I guess I'll scratch the 6750m.

I know I probably could purchase an new iMac but this is serving me well. I'm looking for ways to make it better