The differences in actual recording quality are quite minor to non-existant. In my personal experience, I'd rate them in this order of audio quality (YMMV):
1. Magix Samplitude
2. Sony Soundforge/Vegas, Steinberg Cubase/Nuendo (tie)
4. Adobe Audition
5. Cakewalk GT Pro
I have also used Pro Tools, but only in other studios where a comparison with other software was not possible. But the range from first place to fifth place is extremely narrow; many untrained ears may not hear any difference at all.
Stick with Sound Forge and you'll do just fine. And don't worry about the outdated version for that purpose (I still use version 6 myself); they just keep adding bess and whistles and gadgets to the software, but the main engine remains the same. If any of those extra gadgets are something you feel you can actually use, then sure, go ahead and upgrade. But if you're just looking to capture live recordings and do basic editing and mastering of them, what you have will work just dandy.
G.
