As you heared its more expensive and more powerfull, the reason for this is :
AS5300 CPU 150MHz/512KByte L2 Cache, 16 Flash Max and 128DRam Max, Data or Voice (not together)
8E1s in Data mode and 4E1s in VOIP Mode
4 Serials (2Mbps Max speed per serial), 1x 10BaseT, 1x100BaseT
Router/Access Server
AS5350 CPU 225MHz/2MB L3 Cache, 64 Flash Max and 256DRam Max, Data and Voice on the same modules,
8E1s Data/VOIP , 2 Smart Serials (8Mbps per serial), 2x 10/100 Fastethernet
Router/Access Server/Signalling
Good Luck!