Heyas, Deathwind here. I'll do my best to explain the differences. For the most part each one is a substantial step up from the previous one. Some cards vary slightly so these numbers while close, might vary slightly depending on your exact model... ie: if you get one that is superclocked or some such. One thing not listed below is the amount of memory, but all three cards you linked I have the same 1 gig so for this comparison it's irrelevant.
Here are the major differences:
Video card type: 8400 430 450
Core Clock 520MHz 700MHz 822MHz
Shader Clock 1230MHz 1400MHz 1645MHz
Stream Processors 8 96 192
Effective Memory Clock 1200MHz 1400MHz 3608MHz
Memory Interface 64-bit 128-bit 128-bit
Memory Type DDR3 DDR3 GDDR5
The core clock and shader clock is the processing speeds. The higher the number the faster it is. It takes a difference of about 100 MHz or so to really be noticeable with the naked eye. The stream processors are what do the work to interact with the main processor. The more there are the more information it can feed to the core at the same time. The Memory Interface is the amount of through-put the memory can tackle at any given time. The processors process, but it still has to funnel through the memory interface to be able to render. The memory type pretty much gets faster the newer it is. DDR5 is the newest / fastest. DDR3 is older and slower. DDR2 is older and slower still, etc.
Bottom line? The 430 seriously has a faster clock, 12 times the processing cores, and twice the interface through-put. It will be quite a bit faster than the 8400 and more powerful to enable higher quality graphics. Much so. The 450 has twice again as many processing cores and faster memory clock so load times will be quite a bit faster than the 430, but the interface is the same 128 bit, so the overall graphic improvement is a narrower margin between it and the 430 than the 430 and 8400. For me though, faster load times is just as important if not more important than the quality improvement.
I realize that the 450 costs twice as much as the 430, runs hotter (the 430 will run hotter than the 8400 too), and requires more power. But it is a superior card to the 430. If you don't want to invest all the extra money, the 430 will be a great improvement over the 8400. Should be a night and day difference.
Hope that helps.
DW
