Should I upgrade my TH to Lvl 8 or not?

I think you should upgrade you can easily get dark elixir to upgrade you barb king in Th 8 (via DE drill).

Kim,

If you've maxed out all your buildings exept mines & collectors plus all walls to lvl7 (or nearly) then I'd say yes go for it. The BK can be done at TH8 easier as already mentioned. I'm TH8 btw and went for it at a similar position to you!

Regards

Ely