I just noticed this post -- looks like a fair amount of ground has already been covered.
I'm not sure if this makes any sense, but small + cheap + powerful in a computing platform is tough -- it's sort of like looking for that f/2.8 lens that zooms from 18mm - 300mm, but you'd like to find it for $500. I think we get spoiled a little bit because computing generally is still getting cheaper faster than photography equipment, but as others have pointed out, it's still really, really common to drop a couple grand on a good desktop solution for image editing.
(my latest build, fwiw)
Now, if you're able to give up something somewhere, you can start opening up some interesting possibilities. I frequently connect to my desktop remotely to do light image processing (rating, keywords, cropping -- stuff where I don't absolutely need perfect resolution). I can do this from my couch or a hundred miles away using my laptop, and there's no reason a tablet wouldn't work great for this, too. All the heavy lifting is still done by my desktop in this case, so speed is pretty fair.
Trying to follow along the posts here, it looks like the main use case for you is just to grab the occasional photo off one of your cards out in the field, right? That's pretty important, IMO, because that sort of changes this from a "replace" scenario to a "supplement" scenario. The "upload" bit is sort of key, too -- it sounds like that's a pretty critical part of what you're trying to do, so connectivity is really important. Do you have something in mind in that respect (ie, are you happy with WiFi only or do you need to look at a 3G/4G-connected device)? I'm sort of picturing you posting a couple previews to FB or whatever with "look what I'm doing today", and then going home and doing your "real" editing later -- is that close?