In a couple of weeks I need to travel from Clapham Junction to Finsbury Park using Oyster. The National Rail 'lookup' gives the obvious route changing at London Victoria for the Victoria Line. However I really dislike travelling on the Victoria Line mid-summer as it is usually like an oven. So whilst it's probably much further/longer would it be valid to travel on the overground from Clapham Junction to Highbury and Islington then just do the 1 stop final leg on the Victoria Line. Time isn't an issue and I would much prefer the overground route.