Photoshop :: How To Speed Up Brushes

I'm running an older system (WinXP 32-bit, 4 gigs of DDR2 RAM (733 mhz), lots of hard drive space (more than 1TB), 1-gig video card (ATI Radeon 4xxx series), 3GHZ intel dual-core processor, Photoshop CS5
 
I do a lot of painting, and some of the brushes I have are a lot slower than others. Example- some brushes produce almost no lag, while others produce severe lag. (The slower brushes tend to have a lot of settings in the brush panel such as texture, scattering, dual brush, etc)
 
I'm planning to upgrade my system soon - I'm considering 8 gigs of DDR3 Ram (2400mhz),  a 3.4GHZ i5 quad-core processor, an upgraded ASUS motherboard, and probably stick with the remaining hardware for now. I'll eventually move on to 16GB of RAM. I will also be using a 64-bit version of XP and maybe even go up to Windows 7 64-bit (If I can set aside the time for all the headaches that come with something new like this)
 
My question is, with an improved system like this, would I expect to see the lag drop significantly on these slow brushes? Or is it just the brush itself which is slow and an improved system will have no impact? I do very little in the way of filters, 95% of my workflow is pure painting with a variety of brushes and not too many layers for the most part (usually less than 50 and closer to 10 on average). So my main concern is trying to remove the slowdown when painting.