I thought the biggest difference between 2805 and 3805 was the remote -- the 3805 has this huge honkin' remote with a screen about the size of my PC monitor, while the 2805 has a normal remote with no display (or almost no display).

M60ti, VP180, QS8, M2ti, EP500, PC-Plus 20-39
M5HP, M40ti, Sierra-1
LFR1100 active, ADA1500-4 and -8