2mm fits well on the front side of the VRAMs. For the back, probably 2.5mm would be the ideal size but 3mm works well too, especially if you go with soft thermal pad.
GIGABYTE NVIDIA GeForce RTX 3080 VISION OC 10GB
VRAM front: | 85x45x2mm |
VRAM back: | 85x45x3mm (or 2.5mm) |
Pads on the side: | 1mm, 1.5mm |