I'm currently on lvl 28 with my char and I did the "mixing option". I had a 5 lvl gap at the stronghold, and i farmed there for like 2-3 hours (I am NOT a patient type

). After that I closed the gap to 2, coz i wanted to boost up some skills. Then I kept the 2 lvl gap, but when getting to the Chakji's (or nearby) in Western China I raised the gap to 6. I farmed for sp's quite a lot on Demon Horses and on Ghost Soldiers. Then I got it back to 2...
That's how i want to go through the game. I think it's quite a fair system because I wouldn't hold out like 2 days of pure farming for sp's. I would go

. That's my experience from the mixed system.
Hope this helped you

.