Really impressive and that's not just empty praise- I can tell you quite specifically why I think you should be incredibly proud.
When I got to eighteen miles I felt pretty dreadful. Nowhere near as bad as you but I felt utterly despondent that the only two options were to bail out or keep going. And the trouble with keeping going was that is that it wasn't just going to be a few minutes more of pain, but well over an hour of feeling broken.
Every cliche associated with marathons comes alive when you are tested and find the inner resources you never really knew you had. And although I hate the song, (and stand by with the sick bucket), it is a case of searching for the hero inside yourself. Or strapping on the Man-suit as the Marathon Talk guys would describe. When I emailed my sponsors to thank them I said
"I won’t be doing another. I was tantalisingly close to running under four hours but chasing a time would seem to trivialise the whole experience. I was pretty much at my limit at the finish and felt like death. I am not as big a wuss as I have always assumed and that’s enough for me."
As I mentioned earlier in this thread, I didn't have any significant hiccups in my training or on race-day so am happy to bow out of this marathon m'larky. You though, sound as if you've identified a handful of variables that are amenable to change, and I suspect you'll address them and get a sub-4 next time around.
So, as for this thread's starting point: what are your thoughts on your race-day pacing?
I think that sounds a really good approach- being clear about your pacing for the first half will minimise the venture into the unknown that the latter stages represent.
Early on, you may feel tempted to go faster than 9:45 but I would caution against that. You will need to dig in from some point in the final third: that is inevitable and is what makes the marathon the challenge it is. I felt able to grit my teeth and keep going not just because I knew the fatigue was inevitable; but far more importantly because I could quel the voices that said "Walk, you fool!". I gained enormous psychological ballast knowing that I had run the first half at an appropriate pace and fuelled/ hydrated sensibly.
The other mental strategy that worked for me was to create a personal narrative beforehand: I looked back on races where I had finished strongly, or other life achievements where I had kept going whilst others faltered. The pain of other runners, surrounds you in the final miles. As I pushed on trying to pick them off, I would keep saying to myself "This is what I do".
I'm aware that much of the above might sound like unadulterated cheese but I do think there is enormous benefit from trying to prepare mentally once all the physical graft has been done.
The big proviso though for you will be your knee- I'll cross fingers for you on Monday.
My training programme was taken from the book "Run Less, Run Faster", aka the Furman Institute's 3 + 2 schedule. I mention that because with only three runs a week, the long run is deliberately set at a tougher pace than other programmes.
For all of my long runs, I would manage a target pace final mile but there would almost always be a drift in pace after 16 miles. After the marathon, I was at a ten for tiredness- utterly drained and had to be ushered to one side by the St John's. Post long runs, I would perceive my tiredness as about an 8, but calibrating it now in relation to the marathon's exertion I would go for 6-7.
I was exceptionally lucky in terms of injuries not hampering training.
I'm sure you'll have it covered but my one piece of advice would be to be as clear as possible about your final week and race plan. There is an enormous psychological boost that comes in-race, from telling yourself you are well prepared and your body CAN cope, despite what the Central Governor is telling you.