if you have the technical knowhow and dun mind the risk and time involved, there's always open source software.

Both of those will suffer a similar performance hit when running on a full HD. The fact is that data seek times - and consequently performance - improve when the drive is not so full. This is true across just about every file system out there and not specific to Windows, NTFS or any other MS-specific bit.

Back in the day memory or processor power were the limiting factors in performance because they were the throughput bottlenecks in the computer. Today it is the hard drive. The performance diffrence running the EXACT same applications/OS on the EXACT same hardware, changing only the HD performance metrics is absolutely real and significant. A 4200 RPM HD versus a 7200 RPM drive yields a completely different user experience, much more so than upgrading from 2GB RAM to 4GB or from a Celeron to a Core 2 Duo processor.

ccleaner and jkdefrag.

It certainly doesn't fly, but it's better.

Just put you data files on a different partition (even better, drive) and you've just solved many problems.

Yes and no. Even with this approach a full "data" volume will slow down performance noticeably. The base OS performance will be better, but when you try to actually use any of the data you'll still notice the problems.