Upgrading from 2x 3090 - what should I add? (2x A6000/5090/48GB 4090?)

I'm in a position to upgrade from the classic dual 3090 setup to something that can run the next step up, eg 100-110GB+ model files. I've got an asus x299 ws pro and a 1600w PSU, with 128GB ram, and I want to add to my 3090s, rather than replace them. I'm trying to weigh up modded 4090s (2x48GB), 2x A6000s, or 2x5090s. Anybody made similar hybrid setups with these? Any thoughts on what's going to get me to where I want to be (which is basically a useable quant of DeepSeek V4 flash, at this point). submitted