Yeh, give it a go. I did the 2010 london marathon with tonsilitis against the advice of doctor/wife/most people! but I'd raised quite a lot on money so dosed myself up on antibiotics, pain killers, lemsip and sore throat sweets and finished in 4.05 so only about 15-20 mins worse than I was hoping for...... I did feel very poorly at the end though and wouldn't do it again on anything more than a light cold. I would say start slowly and see how it goes. Good luck.
I agree on the 'go slow' method for the long runs while marathon training, for head and body! When I start nice and gently (9 - 9.5 min miles) and force myself to keep the pace down, it makes me feel much more confident that I can hold a steady pace for the 2-3 hour training runs, and for me that's much more important than speed. My only fast'ish long runs are close to end of training when I do either the Ashby or Oakly 20 race at my hoped marathon pace.
I've flirted with this thread a bit over the years, but used to post more on the 3.45 thread that seems to have pretty much moved to Face Book now. Good to see a few old names still runing and good luck for a quick recovery to all of you with various injuries, tweaks, groans etc. I haven't run a marathon since London 2012, but much to my supprise got in on the ballot system for 2015, so here we go!! I've had various small annoying injuries in the last year or two like achillees tendernitis, stiff ankles/big toe and a knee cap ache that I thought had finished my running but after 18 months seems to be repairing?? but running ok again now so just slowly building up mileage now. Can do about 14 miles but at a slow pace. Club runs up to 10 miles are at 8.00 - 8.30 pace, so going ok. My PB is 3.45 (London 2010) so will be aiming to beat that if I can stay uninjured? All the best with your training folks, and looking forward to reading progress reports.