Go to 6.3.8 if possible,
But if you need more licenses you wont get it unless you go to 7 or 8.
If you go to 7 on your LSP's and ESS's you dont need extra license. If you go to 7.1 it is required AVP licenses on a weblm.
Same in 8.
There is no issues bringing all the survivable to 8 when the core is 6, I have this here at my lab env.