To be sincere... I recommend that you should have started SP farming or as you call it "grinding for SP" when you began in lvl 1 ^^. Since that lvl maintain a gap of 6. By the time you get to your lvl and higher ones ull have a decent amount of SP. But well since you didnt do that

Hunt the mob you feel comfortable (one that doesn't make you waste too many pots per kill so you don't waste gold as much) and keep it with a gap of 6 but for your lvl 7.
P.S.: If you'd like to get A LOT of sp more than exp and u dont mind getting lil xp... then try a gap of 9 or 8 as u prefer hope i helped.