Adaptec 4800/4805 vs 3805 ("unified serial"?)

whats the difference?
4800/4805 look identical to each other except for pci-x/pci-e interface.

The 3805 is listed as a "Unified Serial™ controller", apparently optimized for both SAS and SATA performance, but doesnt the SAS-based 4805/4800 offer 3 gb/sec performance to sata as well?

im in the market for a card that can run both sas (raid 0) and sata (raid6) arrays on a workstation-based mobo.

also any major deal killers in these adaptec cards vs the areca 1680 series (which is prob a bit faster due to using the new iop348 chipset.)

there are a lot of 4800/4805s on the market in the $300-$400 range, and they offer a much better value. havent seen a used arc1680 yet

Thanks in advance!