Matlock,
I was in the same spot as you...choosing between the 3803 demo and a new 2805. My researched showed that the biggest difference makers to me were:
3803 - more power
2805 - Dolby Pro Logic IIx
Because I had inefficient speakers and was more into music than movies I went with the 3803. I got really lucky though (in a way). My 3803 demo turned out to be a dud.
Tweeter couldn't find another 3803 to replace it with so they gave me a brand spankin new 3805 which had even more power AND DPL IIx!
I have 4