Actually, I tend to get a bus or lift to Kentish Town (my folks' house is in a bit of a transport desert - 20-25 min walk from 4 stations on the Northern Line, 2 Overground stations and Thameslink!) so Gospel Oak is just as easy.

I'd looked at Overground > Piccadilly, but always discounted it on grounds of having to double back. Might try it next time

This week I tried a variation on my usual route, with an extra change. Northern Line to Euston, cross-platform change to Victoria and change again at Green Park for Piccadilly. The transfer at Green Park was much longer than I'd hoped. I don't think it saved me any time, but it didn't cost me any either.