Default What's best/current modem used with the i535 GS3?

A friend has been having issues with reception on his GS3. He is on BMB1 while I am on BLK3 but I am on a 4.4 ROM and he's still using 4.1.2. Is there something he can safely upgrade to from BMB1? Is it limited by running JB or KK? I was reading somewhere about the GS3 modems file signature and that you can brick your phone if you flash the wrong one. We are both rooted running custom ROM's.

I'm comfortable flashing from odin or recovery.

Thanks in advance guys.

Verizon GS3: Gummy M3 4.4.4
Wife's GS2: 4.1.2 Stock Rooted
Nook Tab: CM10.2 Dead : (
Dell Venue 8: Stock (junk)
iPad 4th gen: Stock