Toby - good to see you're enjoying the training. It certainly helps.
Curly - next week is my cut-back week, and I'm going to need it after this weeks schedule!
WS - A lot depends on what you have been doing since your last marathon. My marathon time last year was 4:38, and I'm gunning for a four hour marathon in April. I figure that there is no sense in me training for, say, a 4:30 when I know I can cope with faster training runs (based on my 10k/HM race times). I'll get a good picture of what I'm capable of when I race a half-marathon in March.
This mornings run was 9m with the middle 5m at threshold pace. My target for the tempo was 8:16, and my actual mile splits were:
10:21/10:24/8:18/8:18/8:16/8:17/8:24/10:01/9:54
Compared against my previous LT session (10 days ago), my heart rate was consistently 5bpm less throughout the threshold miles 
Feels good to get that one in the bag!