Out of the three products you mentioned, 6000+ is indeed the best (even though the difference is not tremendous). Besides, the prices of these three products are nearly the same so if you seek performances I would go for the 6000+
However 5400+ and 5600+ are 65nm processors whereas the 6000+ is a 90 nm processors which means the latter produces more heat and consumes more.
If you want both performances and economies/stability you may want to have a look at the E6400 or the E6600 which offer same performances as the 6000+ and are 65nm processors.
even though im not a big fan of AMD the 6000+ is a pretty good CPU. but as stated above it will consume more power and will run quite a bit hotter but the cooling fan that comes with it should suffice given that the ventilation is adequate.
it's not like it is going to need a kilowatt PSU or anything but it will draw a little more power than the 5600. depending on what video card and ram and how many fans you have a 500w PSU should be fine. as far as the heat goes, it should come with a heat sync that is sufficient for the CPU just make sure the rest of your case is well ventalated. and don't try to overclock it.
but if you are wanting the most performance for the money then i would go with the 6000.
RAM is 1GB 800mhz DDR2 right now, Ive no idea about video card, will buy in the future because Im not really a gamer.
I guess I understood right that the fan that comes with 5600 is fine, but 6000 needs a better fan than the one that comes with the CPU?
The fan that comes with the 6000 will be fine in that case, the only reason you would need to upgrade would be if you had ventalation issues(which you don't with that case) or if you where going to overclock it(which you won't because you said your not a gamer)
May i make a suggestion on the video card
get a BFG 7950. thats what i have in my work computer and i love it. it doesn't take too much power and it is fairly inexpensive.
you can definitely run all of that on a 400w PSU. i was thinking you where adding a big video card. if you are running on board video or using a smaller video card a 400w will be plenty.