I'd say 'go for it'. I really lost my way at last years VLM, (got a burnt head, drank too much water etc etc) and before long my 9.15 pace had gone right out of the window and I was just running and worrying. Saw the 10 minute pacers and just decided to tail them....kept me going.
The heat got to me way before Mile 20 mate - I am very fair skinned and didnt use any sun cream, so head got quite sore. Also, despite all the best advice I was drinking full bottles of water at some stations instead of sipping. I think I was about 2:10 at 13 miles, then rapidly downhill from then on.
Last year I did the Essex 20 in 2:55 yet blew it on Marathon day with a 4:45. This year I did the Essex 20 in 2:51, and the Brentwood Half last week in 1:52. Everything then suggests i 'can' do very close to a 4 hour marathon, but by mile 18-19 I struggle big time.
So what I'm asking is.....Do I try and stick with a 9 minute pace, which is 30 secs slower than my normal 'half' pace and hope I can keep it going for 26 OR....do I go at 8:30 normal pace and hope I have a few minutes 'in the bank' for emergencies?
Any advice about getting over the 18-19 barrier much appreciated too. Maybe it's in my mind but all training runs and races I seem to struggle from this point. I drink plenty of water and have 3 gels an hour .