Cisco is NOT the best in the world, and they certainly don't put their high end routing gear into Linksys.
Personally, I'd still go with Linksys, Netgear, or Apple (if you already have Apple stuff) for home use.
2.4Ghz and 5Ghz have nothing at all to do with speed of the connection. It's all about interference and distance. 5Ghz will have less interference from microwaves, cordless phones, other people's wireless, but it will not extend as far as 2.4.
Unless you live in Kansas City (or only use the earliest version of wifi), I guarantee that your internet connection is slower than your wireless connection.
I hate DLink as well.
As far as upstairs/downstairs, like everyone else said, split the connection AFTER your router, not before. Use ethernet or wifi to get from upstairs to downstairs.
DON'T... call me stupid!