@350 it crashes in under 1 hour (hard, so I have to power cycle)
@325 it crashes in a few hours (soft until now, so I can restart it from interface)
@300 I'm not sure yet, it crashed once after 4-5 hours.
It is installed in temperature controlled room, 21 Celsius.
Temperatures are 5 degrees under what is it default for batch3 (Temp2 is 65).
@350 impossible due to having 2 fans on system and temp 2 at 65. This was a bad move by Avalon to take the 3rd fan out and redesign the case as its got more air flow going in on Batch 2. Yes it looks smaller and compact however taking 3rd fan out if they have done even with the 4 module version this is very bad.
@325 if crashing after a few hours I would think this is cutting out at a set target temp or something else within the system is overheating. If it is a total cut out then I would advise not using this speed.
@300 4 to 5 hours and still crashing. I would look at air flow control of unit and direct air flow towards heatsynks however seeing on the new layout its almost direct in line with the modulus.
My advise is check to see what PSU it has in it if its anyone branded and no sticker on then I would advise upgrading to at least an 850w to 1000w with that unit. I would also look at tidying the cables up for a little improvement on air flow.
Other than that you might want to look at making a custom case for it that has better management on it or replace the front panel with a new one with 3 fans on providing it would fit it.
In terms of making ROI back on Batch 3 it will be possible however it also depends on how much more and bigger units come online. Currently average is 3 to 5 million increase on diff jumps every 2 days that's giving around 0.3BTC to 0.5BTC each difficulty adjustment. If it goes above this and starts swinging 5 to 8 million then RIO will be impossible unless you are taking your funds and also trading with it.
A solution would be for people to jump of BTC enough for the diff to drop back down it did happen 2 weeks ago but didn't drop by much.