There are some cool, new features of SU 8 Pro (like solid tools and a bunch of improvements in LO for instance) so if you want to try them, I suggest installing it. Do not touch SU 7. Just download SU 8 (Pro if you want to try) and install it side by side version 7. I have 6, 7 and 8 installed (and use them all occasionally). You can even run two, different versions at the same time.
Then if you like 8 Pro, you can upgrade - and yes, I also think it's about $ 95.