Did my final long run of marathon training last night. 20.4 miles in 2:14:56 (6:37 per mile). I had intended to try 6:45 pace, and was right on for the first couple of miles. As I got closer to finishing, I pressed a little, making the last 10 miles a mild acceleration. It felt about as comfortable as 20 miles can possibly feel for me. I think I'm ready to go.
But the marathon is tricky. It's very counterintuitive for me. In races like the 5K (or my college specialty the 1500m), you're pressing the accelerator from the gun. Sure, there's pacing involved, but if you're truly racing, there's no point at which you feel comfortable. My personal experience in the marathon has been much different. For close to 2 hours of running I'm fighting the thought, "I can run faster than this." I want to open up my stride and go for it and I always have to avoid that.
Because as I've learned, even 6:05 pace will feel really easy on race day. Until 18 miles, of course, when suddenly you're walking like a zombie.