In the past, conversations over the upgradability of the iMac's GPU has sparked the interests of some rather talented individuals. I would like to revisit this a year later to see if anyone has attempted to perform the following. Upgrade a 20-inch Mid-Late 2007 Aluminum iMac 2.4 from a Radeon HD 2600 Pro to a GeForce 8800GS. Since I had to tear my iMac apart in order to replace a failed hard drive, I decided to also remove the logic board and GPU heat pipe to properly reapply thermal paste. For all of you who have been reading up on the MBA thermal paste debacle, you'll be pleased to know that it isn't just the MBA with gobs of thermal paste covering CPU/GPU dies. My iMac was just as bad with thermal paste spilling over the die, onto the chip surface and hanging from the copper heat pad. ...anyway. I am rather unfamiliar with the difference between the heat pipe on the 20" vs the 24" and am currently looking for info/pics. Also, if it is possible that the cards are swappable, does the heat pipe sit over the GPU and GDDR to allow for heat transfer? I don't have a 24" to compare with my 20" and most of the detailed photos I've found online point more to 20" teardowns and not the 24". I guess what I'm asking are three things... 1. Is there someone who has worked with 20" and 24" iMac logic boards that may have insight on whether the heat sinks are interchangeable or the existing heat sink on the 20" will touch the right spots on the 8800GS? 2. Are both of these cards MXM-II or III? I'm getting mixed answers as to whether both are MXM-II or MXM-III. 3. An open mind. Warranty is up, machine is in pieces right now. I don't care about heat/power/cost. If it'll fit (and operate), I'm prepared to do this. I'm even possibly considering upgrading the processor to the fastest bus-compatible Merom available. Any thoughts, experiences, etc that you might be able to provide are greatly appreciated.