I feel your pain.
Both TFU:USE and TFU2 ran like molasses on my 2011 system the first time I ran them, even with the latest patches, regardless of my settings. Updating my graphics card drivers did nothing. A couple of restarts of windows later, they magically ran great (well in the case of TFU2 I DID have to do something special.... create a shortcut and add -variableTimesteps to it, I also use the 60 FPS unlocker).
So I was upset at first, but then the problem more or less fixed itself (again, except in the latter case a tweak was required). Now I have no complaints about the technical issues, though once in a great while both games will crash out to the desktop seemingly for no reason (thankfully autosave prevents me from losing too much progress).
Having played a bit of the Wii version (of TFU1), it seems like a rather different game, though obviously based on a similar core, and downgraded to account for the weaker specs. With TFU2 it seems like a little bit of extra care was taken with regard to PC gamers, but at the end of the day both games are basically just a dump of the Xbox360 version. The only advantage we have over consoles is that we are less limited in our controller options, have potentially shorter load times and can access the few limited mods that are out there. PC games have greater potential, but they're obviously just giving out the PC versions as an afterthought. They hope to make their real money on the major consoles. It sucks, but I understand why they do it and I'll take straight ports over nothing.