Any time you move data from one place to another you will have some indexing problems arise. RealPlayer creates a directory of sorts with the path to each track included in playlists, and/or info files. That is how you get a workable Library, and if you have ever moved around files just from one folder to another within your main music folder, you can see how realplayer won't be able to find the moved files, and asks you if you want to repair the missing file paths.
I would imagine that moving the files to a totally different drive may lead to some re-working of your music collection.
The question is, how big is your main drive in which your music collection resides? Also, other than the 5gigs that your music takes up, what percentage of your drive is being utilized by the rest of your system?
If your main drive is 80gigs or more, and you are using 50% of it in total (including music files), then the chances of your music files impacting system performance shouldn't be all that significant. It all really depends on the size of disk you have that determines performance.
If you have a medium to large disk, I would just leave it there, (unless you really need that disk room) and just do a bit of spring cleaning on your disk. Defragmenting your disk would help keep your files optimized for faster access when called upon, and getting rid of the files you don't need wouldn't hurt either. We all have em.
You may also think about lowering the bit rate of at least some of the files if you havn't already. This would depend on the format that you use for your audio files, .mp3, .mp4/m4a, .wma, .rl, .........
If you could post a little more detail, some more specific feedback would surely be available.
Hope this helps,