Personal experiece: During Limited Refinement events it takes me 90-100 med refines to upgrade from 5-7 (80-90 if 4-7) and from there 100-120 adv refines from 7-8.

In your situation, 600 med runes and 230 adv runes, you can possiby do:
1. Upgrade 2 equips from 5-8, eating 180-200 med runes and all of your adv runes. Preferably choose the equips with good initiative purification (purple/gold).
2. Upgrade 3 or 4 more equips from 5-7 with your remaining med runes.