I don't know the time between both maras. Is it a month? or three weeks?
I would train as standard for the sunderland mara, with the taper. I would recover and then aim to 'keep it steady' in the weeks leading up to Edinburgh.
I wouldn't expect to improve your time much for edinburgh ( you never know though, these things just happen out of the blue sometimes) but in my experience despite feeling good on the start line - you will suffer in the last 10k of the second mara. this is the experience of my club mates also.
Eslpeth- i was injured for six weeks over the summer, a few years ago and still did it anyway- so enjoy
Ryan- home you get some kip and rest in the bank after the marathon before number 3 decides to put in an appearance.
the other night, I ran up the hill at skelwith bridge 3 times (as you do....... ), there is one particuarly steep section round the corner- but its mercifully short. tempting though it is to throw in the towel at that point- I managed to keep going. it may be a different story after 10plus miles round them previous hills on the day
I plan to do 16miles this sunday. onwards..........getting close now......