I think there's some misunderstanding here. There is ONLY ONE GAME ON THE PC, and it's "USE" ("Ultimate Sith Edition" which is just the subtitle of "the Force Unleashed").
If you ever see "The Force Unleashed" discussed for the PC, they're talking about USE, it's the same exact game. You can't get any other version for the PC, they're both the same product.
See, "The Force Unleashed" was a single player game released on a bunch of consoles in late 2008. A lot of PC gamers were upset it wasn't ported to the PC. So 1 year later it got ported to the PC, however at that time, the game was also re-released on the PS3 and Xbox360, identical to how it was before BUT with a few optional side missions added. In other words, it was the same single player experience, but you could play some more levels.
When the original Force Unleashed came out, the basic game had "DLC" (Down Loadable Content) that you had to pay for, but they were bonus levels and bonus skins for use in the single player game.
"USE" is just all the bonus features packaged up with the single player game.
There is no multiplayer (only the Wii version had that).
So if you buy TFU or USE for the PC, it's 100% identical. They are the same game, the same product. There's Only One! So you can stop worrying if one will run better than the other, because there's no "other" game to worry about.
Think of it like a movie. Let's say a movie comes out on VHS. Then let's say it comes out on DVD and it has some deleted scenes that you can watch after the movie. You might ask "where is the DVD version of the movie without the deleted scenes option?" but there isn't one. There's only the one DVD. And when you get the DVD you're watching the same movie as was on the VHS, so you're not missing anything. If you don't want the deleted scenes, don't watch them. Same way with the games.
Understand now, I hope?
As for which computers run the game well...
I can't say because I honestly don't know. My computer is from 2003, so it's way too underpowered to even attempt the game (which I don't yet own). I'm only going by what others have said and what information is available. Hardware (processor, RAM, video card, sound card, game controller) is not the only factor... there's also what drivers you have installed and what operating system.
A lot of games these days are requiring 2 gigs of ram, and some even require 4 gig. If you have Windows Vista or Windows 7, at least a gig is taken up by the OS alone, I'm told. Plus the game needs a ton of hard drive space (a ton, in my estimation... I remember when the top games only required maybe a gig of free space plus that much as a swap file, tops).
All I can say is, if you have the recommended system requirements, the latest stable drivers for your video card, sound card, etc. and the recommended controller(s), and sufficient disc space, you should be fine. If not, and problems happen, you should search the Tech support forum here, or go to LucasArts.com and check their support forum and Aspry media (who ported the game to the PC) and check with them. Anything else is beyond us.
If you don't experience any problems, you're lucky. It's not the end of the world if you do.