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1.5mm Gelid Extreme pads on the front (3090 FE only) is best for proper core to core hotspot delta and highest contact pressure. 1.5mm Odyssey pads cause slow core hotspot delta issues with time! If you MUST use Odyssey pads, you need to manually cut them all out to size first, then compress all of them at the same time, at once, using a flat pane of glass on a flat, clean surface, about 0.2mm manually. You MUST use a digital caliper /micrometer to check your work! Once they have been compressed to 1.3mm, re-trim them as they will now be a bit too wide/long. Also, on the left VRM bank (closest to the I/O panel), make sure the VRM pad strip does NOT cover the SMD caps next to the VRM's as those SMD caps are higher than the VRM's and can not help the already bad mounting pressure caused by the leaf spring (X Bracket) doing all of the work by itself.
Gelid Extreme pads are soft enough to easily compress under the weak pressure generated by the leaf spring. Yes it's weak pressure. Look at an AMD blower card and compare the screw layout. (R9 290X, 5700 XT/6900 XT etc), notice all the screws around the VRAM that help with the compression? The Nvidia FE cards don't have that, except that one single screw on the backplate that is right next to the PCIE VRAM area (which is why that pad always compresses the most--doesn't take a genius to figure this out).
1.0mm pads are too thin. Do NOT use 2mm pads on a 3090 FE front side.
On the backplate side, you can use whatever pad you want. Gelid Ultimate pads seem to be slightly better than Thermalright Odyssey pads. However I would NOT suggest Gelid Extreme pads 1.5mm or 2mm (both do work however, just make sure you use the same thickness throughout) on the backplate side! The Gelid Extreme pads will give you the lowest VRAM backplate temps, however the extreme heat (much hotter than the front side!!) caused by the backplate getting heat soaked will make the pads melt and turn into very sticky putty (this is always an issue with softer pads!). This does not hinder performance whatsoever, but makes the backplate extremely hard to remove without breaking something! If this happens to you, you MUST preheat the card to 100C (either by running a miner or something, or passively heating it with a hairdryer to 85C+) and then quickly disassemble and remove the backplate, which will then come off much easier (still sticky).
Apparently on 3080 FE's, 1.5mm Gelids appear to be too thin on the front side, unlike 3090 FE, so for 3080 FE, 2mm Gelid Extremes can be used. I'm guessing something about the heatsink dimensions are different.
