Which GPU for video on Mac Pro?

I have a Mac Pro 3,1 which I use for music (Cubase) and also for video, although the latter is a struggle because of the ATI Radeon HD 2600 video card.

I'm thinking of updating the GPU and find choices bewildering! I'm using Premiere Pro (CS4) and sometimes After Effects (CS4) but even 720p videos take forever!

So can anyone recommend a GPU? I gather a 3 or 4 GB card is best, but not sure whether it should be ATI or nVidia, or something else. I'm aware it shoud be flashed if I want EFI boot screens (I am planning to update the Mac Pro to a 5,1 as well).

The fans need to be pretty quiet as well. Any recommentations would be most welcome, as I don't want to blow lots of cash on something that won't work with my current setup.

(Before anyone says "get the M1 Mac Mini", I'd love one, but I'd have to update all may software and buy in some racks to hold all my hard drives. Maybe one day!)

Thansk,

Graham.