TL;DR: I'd take the RAM. Which I was going to say when you asked, but then I had to check a bunch of benchmarks to be sure, because I Have A Problem(tm).
This is another place where Steam Deck changed my mind. The OLED I bought has a nice bandwidth bump, and yes, it does improve performance, and it doesn't matter. It smooths out dropped frames in some games, in some places, but it doesn't make them go away. And it doesn't give a high enough performance bump for you to up the frame cap or increase visual quality.
The extra RAM means you that regardless of the frame rate, or even the resolution you're looking at highest quality textures. That's a
definite win. But AMD and Nvidia are obviously different architectures, which is why I had to check benchmarks.
The 3070 is one of the more bandwidth starved cards in the RTX 30 line up. The 3070 Ti has only 6% more compute power, but it's got a whopping 35% more memory bandwidth, putting it on the high end for bandwidth. Digital Foundry has a bunch of benchmarks for these cards, and... it's 6% faster. Slightly higher on 4k games, but lower on 1080p games. Same on the RT benchmarks.
The 3080 has a 12GB version that is much the same. Only 3% different in TFLOPS, but a 20% increase in memory bandwidth... and a 6% improvements in actual games, disappearing quickly as you drop to 1080p.
I'm sure that software developers optimizing for the hardware could do amazing things with the extra bandwidth. But it doesn't look like existing engines are really hitting bandwidth limits on Ampere hardware, so staying in line with the rest of the RTX 30 series seems like 3rd parties will be in great shape. And as for first party stuff,
Nintendo has the most bandwidth optimized engine on the market. What they're doing with
Tears of the Kingdom and 25GB/s of bandwidth is insane.
Side Note: Since I have all these benchmarks and specs in a spreadsheet (I SAID I HAVE A PROBLEM AND THE FIRST STEP IS RECOGNIZING IT) I decided to look at the less sexy parts of the architecture. ROPS, TMUS, and the L2 cache. All of these systems interact in various ways to create the final efficiency of the system.
There are folks hoping for 4 MB of L2 cache, and not the 1 MB (as the leak is ambiguous). If you look at cache as a proportion of the memory bandwidth available, 1 MB is already more than any desktop card. 4 MB would be beyond generous, and likely pretty expensive. 1MB is already luxurious.
Texture mapping units are part of the SM design, so the ratio there always matches. Sufficient or insufficient, there is no way to tell, because it's locked into the Ampere/Lovelace design.
ROPs are a little different. They're by GPC, so sometimes you get extra ROPS relative to SMs after binning. With just one GPC, that isn't happening on T239, but it also doesn't seem to matter, Performance doesn't seem to track with ROPS in a way that indicates it would be a problem.