The MB4 modem is not the LTE updated modem. When it is available, a new modem will be uploaded by one of the many great devs we have here on XDA. Latest PA, plus MB4 does show a massive signal difference, and D/L speeds tripled for me. I would go for it.
TerrorCandii Inc.
I also have the aboved combination. Latest PA and MB4 modem. Should I still set the mobile networks to LTE / GSM / WCMDA?