There's a V50 runner in my club who always races a 20 mile race around 4 weeks before London and it doesn't seem to adversely impact his marathon - he still knocks out 2:32/2:33 times. But I think he is unusual in that he seems to recovery easily. In my first marathon I raced a 20mile race 5 weeks beforehand and it didn't seem to impact my marathon. It was also a great confidence booster. But in my last two, I have used the race in place of the P&D session with 20 miles including 15 at MP. I don't think I'd fully race one now, more because of the injury risk than the recovery required.
Scott - your 10 mile and HM times are similar to mine but your 5k time is much faster (especially if you think you can knock more time off) so I reckon more miles over a consistent number of months and lots of long runs should get you your GFA.
Big G - if it's on the fridge there's definitely no going back! I think Shades is right re swapping sessions around. For example when I had my 20m race, I used this for the 20m with MP session so just brought the session forwards a couple of weeks. And I counted my HM as one of the tempo runs (except all at HM pace) so shifted things around for this. This was the one race I did taper (but only built in an extra day's rest) for as I wanted a PB.
Shades, good to see you are on the mend. You seem really good at listening to your body and knowing when to rest. Races can be expensive but still good value compared to a night in the pub!
Cal - hope the heel niggle disappears. I've picked up a small knee niggle today, probably due to all the hills around here that I'm not used to! Been on a boat trip today where we saw lots of seals. The sea was a bit choppy! Then afternoon spent crabbing on the harbour wall. I had to go and buy more bait as a greedy gull stole our bag of bacon that we were using!
Big G - I wasn't strict at all re the order of the sessions, although I did always do the long run on a Sunday. I tried to avoid having consecutive days with the harder sessions though to allow for recovery. I think the races built into the plan are on a Saturday as this is when races take place in the US so that obviously means changing things around too. There was a good interview with Pfitzinger on Marathon Talk a while back if you haven't heard it already. I think the one thing he said he'd change would be adding more strides!
Well done on the PB Jugula, hope you enjoy the rest of your time in Spain.
Shades - sorry you've had to DNS your race, get well soon.
Also, just to add, if you look at the plan as a whole, it can seem quite daunting because of all the speed sessions. But I found it's easier to just take each week at a time as there's usually just one tough session a week and sometimes you may want to replace these with a race or a parkrun.