Not sure where you got the 256/128 numbers, unless you're citing old HN9000 numbers. Gen4 customers served via the slower Spaceway 3 satellite should still be able to obtain 800 Kbps uploads. It's still the same satellite, but the modem is different. Gen4 customers on Spaceway 3 get the HT1000 modem, which bumps the transmit (inroute) speed to an advertised 1 Mbps.
They may
advertise 1 Mbps (or 1000k) uploads, but in reality that number represents the symbol rate; 1 Msps (or 1000 Ksps). Clear day inroute correction rate is only 4/5 (1 redundant bit out of 5 transmitted) gleaning about 800 Kbps out of 1000 Ksps. But as propagation conditions deteriorate, the ModCod rate steps proportionate with attenuation. In inclement conditions, as error correction increases, data rate decreases. Worst case scenario could gradually step your transmit speed to as low as 64 Kbps, but the decreased speed relative to increased error correction is what keeps your connection alive as long as possible.
//greg//