Well, I cannot change the wiring, that is out of my control.  The electricity is free but it has to be 120 volts only, unfortunately.

Anyway, the S9 can work on 120 volts just fine it appears, from all the various threads I've read.  (on 20 amp anyway; 15 amp is pushing it)  Maybe not much room to overclock, but 1400-1500 watts is pretty much a bit less than a space heater or many hair dryers on high (hair dryer is short term load I know, but space heaters are not, and I have many running in winter 24/7 with no shut off time at all).

Z11 wattage seems to be right on the edge of doable on 120V/20 amp... (1580 watts?)  I could do the minis to distribute the load better, but they are not cost-effective.

Glad you mentioned that Braiins OS - is that preferable now to that bulldozer one (don't remember the exact name) or ASICBoost (https://support.bitmain.com/hc/en-us/articles/360011930734-ASICBoost-firmware-for-Antminer-S9-series-and-T9-)?  Also, I read somewhere that newer batches don't allow custom firmware?  But also seemed that meant, they cannot be reflashed, but you can run custom firmware from SD card still, is that accurate?

I do tune my GPUs to fit better on the PSUs I have, so if I can count on being able to do that on S9, that would be sweet!

Final question - you say plan on a year to ROI?  The SHA-256 difficulty is not rising as fast as it used to though... Right now whattomine estimates $4.30 a day for 13 TH/s... rounding down to $4, that's $120 a month - even if I pay $600 per machine, and difficulty rises 25% in six months, I think by month 7 they're covered?  (don't forget, electricity cost is zero)  Or you think difficulty will still somehow double if BTC rises?  I was kind of thinking, maybe the SHA-256 hashrate is starting to get to a slower growth - newer machines aren't much faster on a per watt/joule basis... although if BTC goes to $50k, then I guess, sure, any old miner will find a place to get turned on again...

As a whole, I dunno.  It's hard to predict if GPUs will slow again.  Or if they'll magically rise.  (hard to see how, alts are taking a beating every time BTC rises lately, and NOT recovering when it dips!)  It would be a lot more exciting to get several Z11s, but riskier of course since they might double the capable hashrate in a few batches from now.  Whereas S9s will probably retain some decent used value if BTC stays the same, and one S9 at current earn rates would pretty much equal one GPU machine, for 1/5th the cost.

Edit: was just looking at a hashrate chart again - tough to predict.  It did go to all time highs recently.  But hard to tell if it will now grow as fast as it did in 2017.  I don't know if it's possible, if SHA-256 ASICs are slowing their efficiency increases?
https://www.blockchain.com/en/charts/hash-rate?timespan=2years