"99% uptime", on a normal desktop environment, is achievable with any NT era windows and some common sense. That's anything from 2000 to 8.1. Debian is good for server environments, specially those that are more of the personal persuasion. On a desktop environment, having older everything is a huge hindrance that really doesn't pay off in the long run.
If you're feeling adventurous, however, you can try your luck at Arch Linux. If done properly, the system will be as stable as any debian, but with newer shit and much more customizable.
And if you're feeling EXTRA adventurous, you can just slap Xen on your debian machine and put some windows 7 HVM on there. You'd have to look for the paravirtualization drivers and take a performance hit of about 5%, but on the flip side you'll have a really stable machine.
And seriously, sid is a developer build, with probably nightly builds. I'm not willing to do THAT just to have a newer version of certain softwares. Unless you're talking about testing, which is not sid.
And if your problem is optimization, swap desktop environments. My sis' 8 years old laptop runs Mint with the Cinnamon DE, and that thing only has 1G of RAM.