Trying to fine tune my rig and solve a few problems. 6x RX580 only doing 21-27 Mh/s most are at 25.

I'm not sure exactly what's going on with Claymore but I my mining is really inconsistent. Specs:
Win 10 fresh install, genuine.
TB250-BTC board with mining mode turned on.
4x Powercolor RX580 8gb, 1x XFX RX580 8gb, 1x AORUS RX580 8gb
6 usb risers
G4400 Pentium LGA1156
16gb DDR4 ram
Thermaltake 1275 watt PSU
Open air case with two fans and VGA fans on 80-90%. Temps sitting around 48-55 C.

It seems to fluctuate between 100mh/s and 140 mh/s. Goes up, comes down, goes up, comes down, etc. Just curious how I could stabilize it at a higher rate. Sometimes they all drop to 1-6 Mh/s per card which is strange.

Also, all of my cards are normally:
1x 23-25Mh/s, 2x 23-25 Mh/s, 3x 26-27 Mh/s, 4x 24-25 Mh/s, 5x 20-21 Mh/s, 6x 24-25 Mh/s

All of them are bios modded except for 1, the XFX, which was a 256kb file.
I was expecting a bit more than just 25 Mh/s or 150 Mh/s for all 6.

I've been building computers for a while now but this is my first mining rig. Could someone help clarify if i'm doing something wrong here?
Anyone know how to bios mod the XFX 256kb card?
Was expecting at least 27-30 for all 6. Overclocking with Afterburner doesn't seem to yield me any different results.