probably not much. you are steppig up the number of cores but dropping 100mhz in speed. Some apps & games wil lbe able to use the extra cores and some wont.
Windows itself should feel better as it can multitask much better witht he extra cores. Alot depends on what you had running in the background when you gamed. If windows can move stuff off the gaming core(s) that previously had to run the game and background stuff then yes you will see a difference. But if your games are single threaded then probably they will be the same.
The X4 Deneb not only have more core but more cache memory to help in gaming... But what is your LCD resolution? If it is not too high, you can even get the X3 720BE. I used to have an X2 5200+ and upgraded to this to pair up to my HD4890. All applications runs very smoothly in this combo.
By the way Popatim, the X4 925 is 2.8Gz or 200Mhz faster than the X2 5000. So with more cores & 200Mhz more on stock, the X2 5000 offers no contest at all.
Well, the 720BE can handle that sure enough. I got my 720BE 2.8GHz running my games at 1920x1080 at highest setting and it does not falter a bit... Should be enough for your 1680x1050.
That is if you want to spend for only what you need. Unfortunately, I see there is no stock at newegg currently. If you want to save some $40, go for the X4 630 which is $101 free shipping. Its the same clock speed as the 925 but with no L3 cache. It shouldn't make much difference in many applications.
For games the L3 cache does make a difference. Anyway, I went from an Athlon 5000X2@ 3.24 GHz to my current Phenom II X4 955BE @ Stock 3.2 and I got a significant improvement. Games that only really used two cores saw a noticeable improvement, and of course the improvement was much greater in games optimized for quad core CPUs . I'm happy enough with my CPU for now and won't get around to overclock it till I upgrade my video cards and need the extra power