<< what's the performance increase from 256megs to 512 & 768 megs? >>
Unless you are running heavy graphics apps (Photoshop, CAD) with lots of stuff in the buffer or acting as a server I don't think you'll notice it. Just for grins I decided to start a bunch of applications to see when I would start running into trouble on my Win98SE FIC VA503+ with 192 MB of PC 100. I opened Corel Draw, several Office suite apps, several browsers, Outlook Express, Norton Utilities, MS Picture It, Photoshop, Quicken, several other unwieldy programs while paying MP3s with Winamp. I still had 40 MB of free RAM. Now granted, I wasn't actually DOING much with most of these programs, but I wouldn't ever use my computer like that either. I rarely have more a few programs open at once, say my mail client, newsreader, music program or TV card, spreadsheet, word processor, several browser windows, and one or two graphics programs, and of course, numerous background services (firewall, anti-virus, maybe Seti, MSN Messenger, Winkey, etc.), while maybe burning a CD-R or ripping a CD. (Jeez, I guess I am a memory pig!)
But, with memory this cheap its tempting to load up those slots, particularly if you run NT, W2K or Linux. W2K Server is a particular dog. Still, I didn't notice a speed increase on my A7V W2K machine going from 256 to 768. It is back down to 256 again, though it'll probably climb again when I can find 256 sticks of high density for <$30 delivered from reputable vendors.