afaik, they're identical except for the SSD and an anti-glare coating on the 512gb one.

If you're comfortable opening them up, you can upgrade the SSD yourself. it's a standard m.2. I think there's a lot of online videos and docs on how to do it. THe benchmarks i saw found many m.2 ssds run faster (and slightly warmer) than the steam one.

If that's the case, you can probably swing the 64gb and call it a day. it's a pretty great deal for that.

If you're not into that, it depends on how many games you want installed at the same time and what type of games you want to play.

Just get a decent 1-2GB SD card for the 64 GB deck. Uninvasive, convenient, cheap storage upgrade with no human-noticeable performance difference between the more expensive decks.

I've owned both the 512 GB and 64 GB deck + big SD card and I can't tell the difference between them without precise performance benchmarks. The only difference is the 512 GB has an anti glare screen.