Capital growth and yields are not the same in each part of London. Where yields are high in some area the capital growth is low.
For established areas with good yields try Maida Vale, W9 or West Hampstead, NW6
There are several areas in London that combine capital growth with good yields and Islington is one of them, another one is Haringey. Within those areas I would be looking at Hillmarton, Lower Holloway, Harringay Ladder, Strode Green. All of these areas boast superb transport links and are strongly heading in way of gentrification.