said by OHSrob:But that is because you were using MLPPP. That is a different scenario. MLPPP allows for fragmentation and reassembly. Thus allowing for much much larger frames to be passed down the connection.
Caneris's ML-PPP implementation scales very nicely to 16 lines as well. They have one of the most reliable and versatile LNS I have ever had the pleasure of connecting to.
edit: I never tested an MTU of 1500 on a single line, it was always on 4+ lines.