Having some issues with the Silverfish, either chained or not chained they seem to only stay at full speed for a very short period of time, then slow down over 4-6 hours, and then speed up again, and repeat.
Two things I can think of. What is temperature like? It seems to be more susceptible to heat with open air then the A2's with closed case. With 6 in a row without extra cooling this most likely could be it. Looking at setup of 6 pulling air from against wall so close together and no extra fan's or cooling I think this is best bet.
The firmware would be second thing to look at. What does your second tab in the blades go to, does the performance (M) go to 14 and level there? Old firmware seems to not level there.
Edit i should add this just so it's out there in-case anyone else needs this I didn't mention earlier as your mining experience is difficulty level. But the difficulty level on pool needs to be set high enough to optimize the asic miner. If difficulty is to low it can cause high variance and low hash rates.
Temps are less than 55 , so not a problem. The are pulling 65f air right from an over head AC you cannot see in the pic.
Firmware is the latest, and is at '14'
Diff is set correct at the pool level.
I now have 2/6 blades showing a dead blade out of the 2, and they still do not remain hashing stable for more than a few hours.
As Mr. Lee noted up above it does seem some blades have a lower hash rate.
I have mine very cool, that personally helped me on stability. I cannot speak of dead blade, as I have not had a unit to test with that. They do tend to have a higher variance depending on blades and in my case temperature. It is cooler then I keep the rest of my miners. I had it pointed at clever yesterday because of pay, personally waffle I tend to get a little higher with on this SF. But the pay was so good I used clever.
Here is pictures of one mining with very very cool air temps, in mid 40's c about 10 degree C under what you mention. You will see it only needed restarted once in a day, I didn't catch it right away so you will see it run lower for a little bit and it did effect average and pay. I can say personally temperature and the new firmware helped mine greatly.
The very cool air being used is shown below: