How many peppermints do you have? They're known to hunt in packs and the more the better. I just added 4 to a 40g and they cleared out the aptasia in 2-3 weeks. I would imagine 9-10 would work in your tank. The sponsor NEMO is currently selling them at $5 a piece (I just saw that Love the Reef is selling them for $15 each!). I've not had success with Berghia nudibranchs but others have. A copperband butterfly is also know to work but can be hard to acclimate - though feeding them whole clams seems to help. In my experience aptasia eating filefish are completely useless, though others may disagree.
Good luck! At the end of day aptasia are a pretty minor nuisance, don't let them bother you too much, everyone has them - it's mostly about control rather than irradication.