Don't go with the Yeti DH bikes... They're sick and awesome and everything, but the rail takes SO much maintenance. You'll spend more time cleaning and greasing your bike than riding it, and it'll go to shit if you don't maintain it.
If you want to have a really awesome, quality bike, take a look at Santa Cruz's offerings- the Driver 8 and V10 are both really sick. I've ridden a well built V10 and it was the best DH bike I've ever ridden.
Spesh Demos are really nice too, some people love them, some people, not as much. Haven't ridden one, but my friend has one and he loves it.
Giant Glorys are fantastic- I love the way they ride, but they aren't the most stable bike in the air.
Devinci Wilsons are known to be good as well, but I can't speak from experience.
Commencal Supreme DH - Commencal makes sexy bikes that seem to work well for the Athertons, and I haven't ever heard a single bad thing about them. Plus, they have the deal with BTI where you can choose your own part spec - down to the chain, tires, bars, colors, grips, and everything. It's the whole shebang, and the price comes out reasonable. You can build it under $5000 depending how you choose parts. Here's the link:
http://bti-usa.com/public/build_a_bike/1?build=AABB1B1B-3859-4E12-A8AB-8B6194D847FC
As for your fork, go for either a Fox 40 or Rockshox Boxxer Team (minimum, don't get the Race. WC is nice, but since its air, it's higher maintenance, and changes with altitude and temperature). Don't bother with Marzocchi, their suspension is millenia behind Fox and RS.
Drivetrain spec, I'm more a fan of SRAM, but go for whatever you like better. Shimano and SRAM make equally good parts- I'd go with SRAM X.9 derailleur and shifter, with a Shimano cassette and chain.
Since you have $5000, I'd buy a frameset and build it up yourself, unless you find a build you really like to begin with.