Hi Martin,
(Really interested to hear answers to AgentGinger's & Ian Stantham, as I'm in the same boat, in that my target Marathon pace is 8min per mile(-ish see later) & my 10k pace is 7 mins per mile,so running slower than 9min per mile feels 'unnatural/poor in form').
My specific question, though, is around what pace to set off on, for the London Marathon in April. Although my last marathon time (2009) was 4:05 (I got severe calf cramp last 5 miles, which returned every time I went faster than a crawl). My half time is 1:40 & my 10k is 43:50, so all the calculators suggest I could potentially do a 3:30 marathon.
At 54 this may be my last marathon so I'm torn between setting off at 8mpm to try to achieve the best possible time, or a more conservative 8:30mpm (3:45 target) so as not to blow it again & maybe go over 4 hours again! Obviously if I set off at 8:30pace I'll never get near a 3:30 finish, even if I feel good & increase my pace later in the race. So difficult! Can I perhaps use my training times (I'm doing tempo, intervals & a long run at 8:30pace each week & the Silverstone Half in March) to judge the pace I should start at? Or is all that all irrelevant, as I failed to break 4 hours last time?
NB I read recently that negative splits aren't always the best way of achieving a PB, so I'm tempted to try 8mpm & see if I can hold on(?). Please advise a very confused runner.
Thanks