Although Samsung might list different bands I think it comes down to the radio hardware. This is what I do know. My MetroPCS S4 was able to get 4GLTE with MetroPCS service and also with a friends T-mob sim card both pulling around 13Mps down and 9Mps up at the time, sometimes more at night for some reason. After I messed up my MetroPCS 4.2.2 stock ROM from flashing back and forth I had to flash the T-mob FW to my phone. Running the stock T-mob 4.2.2 my MetroPCS service still worked or I should say still works with 4GLTE as there is no stock recovery FW for the Metro S4 yet. I don't know spec wise what exactly Samsung says but I do know LTE works with MetroPCS service when my phone was a SGH-919N and now that it is a SGH-919.
Another interesting point I found was that some custom ROMS allow you to change the radio frequencies easily which is needed for ATT S4's to work with LTE on T-mob. From what I have found I think its more about the hardware then the ROM for FW. Personally the Metro S4 is cheaper and you can use it on T-mob or MetroPCS with ease.