I think i did pretty decently on my 5700 rig... total GPU cost of $2,150 for 4 XT's ($373 avg price) & 2 non-XT's ($330 each)... and all of these purchased in the last 10-12 days.

Absolutely agree with Phil that waiting for 3070's is not a good plan. First and foremost, we could (i hope not) be back to low block rewards by the time you get those up and running. The name of the game here is mining as much as possible when profits are at their highest, so sitting out a spike is simply not a good idea.  Furthermore, since when have Nvidia GPUs been even close to Radeon for mining profitability/days to ROI?  Maybe the gap was a bit smaller when ETH was way down and dual mining other algos on Nvidia could make decent returns, but certainly the hap is large now with ETHash being the most profitable GPU-mining algo by far!

It will be very interesting to see what happens when all of those 4GB cards cant mine ETH any more.  I will run my new 5700 rig in addition to my four 6x 470 rigs and 2 1070ti rigs and that will get me around 1.3Ghz on ETHash.  Assuming profitability holds a bit longer, I could see building 1 more 5700 rig in time for the Dec deadline, which would still get me 1Ghz even after taking those 4 470 rigs offline.  Then, who knows.  From what I've heard, implementation of ETH 2.0 will likely kill off the nice bump in block rewards we've seen recently. But, who knows when that will actually go live?  A lot of variables are in play that nobody can predict, but if things stay good into the beginning of 2021, I would take a hard look at the mining capabilities of the forthcoming Big Nave GPU's.  Even a 30% efficiency bump over 5700's would make things very interesting!