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I'm skeptical that you'd be able to reliably get 55th on all those t17s. The stock T17 is already overclocked... it is exactly the same chip as an S17 except run at higher voltage and frequency per chip. They put fewer chips per hashboard and gave them larger heatsinks.
You can pretty much count on being able to get much better efficiency when underclocking though.
If you have someone local who can repair them, I would not eliminate the T17 as a possibility. They are easier to repair than the S17s since they have fewer chips that are more spaced out. And when underclocked you could get better than 40w/th on some of them, so when the market finally catches up you have a chance at still being profitable.
At least in the US, the listings I've seen for M20s are closer to $80/Th for 10 or more miners. Close to double the price of the T17. For that I'd take the risk of the T17, or I just would just keep buying btc and wait for better conditions to buy gear.