I'll be there.... and at both the other races in the series as it happens.
Potentially fast if I recall (the course, rather than me). I occasionally work at CapabilityGreen and the planes are deafening at times on the path just outside which is on the race route. Still it'll drown out my puffing and groaning!
I've done 3 marathons in the Asics (2120 / series ) and one with the lighter DS Trainers. No problems, but I did initially make absolutely sure they suited me by going to a proper running shop as previously suggested. Sounds as if yours may be nearing the end of their life (at least for long running purposes!). Although this sounds sad, I keep a record of the mileage each pair has done and change every 450-500 miles - and I think that's pushing it....
Having said that, at the first sign of the tell tale niggles in knees, lower legs I'd change them anyway as I have noticed that this is a sure sign (for me at least) that the cushioning is shot. Last time I changed I compared old with new and the old ones felt like running on bits of wood in comparison to the lovely bouncy new ones!