For your application I think the buffalo would have done great, but the Mushkin should too. I've got 2x512 of the buffalo 3200 in the machine right now, and I've got 2x512 of the 3700 coming monday to see if there is any improvement. You can see from the cpumark mem score in the sig how much potential cheap ram has in the right circumstance.
I really like having 1GB over 512MB. I too got by with 256MB 9 months ago, went to 512, and got hooked on the snappiness 1GB provides. General browsing and desktop navigation speeds up more than I realized before I tried it. And of course really hungry games like BF1942 really notice the difference.