For the money, the 5800, the 5803, the 4802 IMHO are all better units than the 3805. Everything from the power supply, capacitors, heat sinks, transistors, etc... are all upgraded on those units. Those are flagship receivers.
The 5800 offers DTS ES Discrete 6.1 and DTS Neo 6 - which I prefer over Dolby's similar offerings. You also get THX certification, something the 3805 lacks for some reason.
The 3805 is no slouch, and is feature ridden. But when comparing the 4 and 5 series units, they are in a totally different league.
I own a 3805, and would have purchased the 4802 at the time but it was going for $1300, while my B stock unit was only $740.