Your best bet is to download a trial version and make up your mind ...
Usually new versions are backward compatible, I wouldn't be afraid of this part.
While your there, try a few others..
Many of RO members started to use Magix Samplitude with great results. ;)

I'm currently on pro 10, and all my old stuff works fine each upgrade. My collaborator is on artist 9.5 and we share lots of files. he's just upgraded to artist 10, but I have two see him over the weekend because it didn't install properly. Realistically, some menus have changed, the layout is different - I don't think 8 had the split screens, did it? Clicking on a track opens an editor under the track window rather than in a separate window, and more panels can appear left and right. I think you might get a few extra drums sounds and an update to Sonic too - I only notice these things when they appear on my screen for the first time - sometimes I discover they were in the old version, I just didn't notice.

The only thing that ever trips us up is that I use VCA faders, which artist cannot use, and there's limitations on track count and stuff like that. I'd guess that the other differences for us, are in areas we simply don't use. One thing I did find out from my friend is that installing the new versions but then not activating them when the trial ends gets a bit messy - and he found that he had lots of plugins in different places that each startup cause a reminder to appear, and he's never really sorted this and lives with it. I installed by mistake an artist version, not the pro one - and my damn licenser constantly throws up an error. I've not sorted this one!