Go with the cheapest most reputable seller. If it has warranty get that.
If it's Asus or EVGA lookup the serial.
Also, I'd double check any rtx 2080 ti, but particularly if it's below 900.
I had a strix and it was nice.
You can MTP it when you get a water block, but based on what I was seeing on my core, I was almost temp limited on hotspot. It doesn't really matter though, since I don't run any overclocks while gaming. lol.
3080 lhr models are selling for the same price or a bit more than reference 6900xt's. Those mine at high power and do not even mine faster than 6900xt's.
As for the 6800xt/6900xt, yea, just spend the extra 100 if you are not buying at amd msrp (which is only sold at amd nowadays).