[beamer4]

My current iMac 27" Core i7 4.0 5K, Late 2015 machine has an AMD Radeon R9 M395X graphics processor with 4 GB of GDDR5 memory. The spec's on this graphics processor indicate that the bus interface is "MXM-B (3.0), and its memory bus is “256 bit”, with a TDP rated at 250 watts maximum.

So, Choice # 1: Can I swap this out for a AMD Radeon Pro 580X with 8 GB of GDDR5 memory? The main difference is that this processor has a PCIe 3.0 x 16 bus interface. Its memory bus is the same “256 bit”, and its TDP is rated at only 150 watts (would this mean that there wouldn't be overheating issues, because of the lower power consumption?)

Choice #2: What I'd REALLY like to do is put in an AMD Radeon Pro Vega 64 graphics processor with 16 GB of HBM2 memory - this also has the PCIe 3.0 x 16 bus interface, but it also has a different memory bus, at “2048 bits”, and a TDP rated back at 250 watts.
Bottom line question - does the bus interface (PCIe 3.0 x 16) and/or the memory bus differences from my existing graphics processor STOP me from making any of these upgrades?
Any knowledgable advice would be most appreciated!

[pkcable]

Other than RAM, iMacs are tough to upgrade. You need to take off the screen and do quite a bit of disassembly to get at the motherboard and such. Lots can go wrong.

[beamer4]

Yes, thank you, I am aware that it isn't easy ..., my question is CAN it be done? Specifically, with the potential compatibility issues involving the bus interface and bus memory details. I would employ a professional (not Apple) to do the install, and since my warrantee is already expired, I may be willing to risk it.
I need to know if its even possible - specifically, will either of these graphics processors run in my machine? If necessary, can my MXM-B (3.0) bus interface be made compatible with the newer PCIe 3.0 x 16? And/or, in choice #2, can my 256 bit memory bus interface be made compatible with the newer 2048 bit connection?
Does anyone know?

[pkcable]

Maybe do a search on Youtube, IF this upgrade has been done, someone probably filmed it, Luke Miani or Snazzy Labs for example, plus there are a TON more that do Apple products upgrades.

[beamer4]

Thanks, yes, I know about Luke Miani, he tried this in one of his spots, and ended up lying on the floor, crying! I'll check out Snazzy Labs!

[flyinion]

I did a little looking and it doesn't seem like there is a mobile card based Vega but maybe an integrated APU (CPU + GPU) of it so you'd be out of luck there. However, if you find the mobile MXM version of the 580X that might work if the OS will support it etc. Techpowerup says the mobile version of the 580X is the same MXM interface https://www.techpowerup.com/gpu-spec...x-mobile.c3235 you might have been looking at specs for the non mobile one.

edit: Possibly important but they list the 395X which you have as having a Mac edition, but not so for any of the newer stuff so even if you physically and electrically get it in there, it may still fail to work on a software level.

[beamer4]

Wow, thanks! I was not aware of the Radeon RX 580 X Mobil ... you are right that the spec's on the bus connections "appear" to be compatible! And with a TDP rating at only 100 watts, heat dissipation may not be an issue. You are likely also right when you say it could connect up all right and still fail on the software level ... and getting an answer to that is certainly beyond me!
If it failed at that level, there's probably no fixing it? Physically trying it out may be the only way to find out, and then I could end up on the floor crying just like Luke Miani!

[flyinion]

Wow, thanks! I was not aware of the Radeon RX 580 X Mobil ... you are right that the spec's on the bus connections "appear" to be compatible! And with a TDP rating at only 100 watts, heat dissipation may not be an issue. You are likely also right when you say it could connect up all right and still fail on the software level ... and getting an answer to that is certainly beyond me!
If it failed at that level, there's probably no fixing it? Physically trying it out may be the only way to find out, and then I could end up on the floor crying just like Luke Miani!

Yeah unfortunately I have no idea on the software side. I run custom built PC's at home so I'm not super familiar with Mac hardware and what you can swap in/etc. and how the drivers and such work.