In total have done 7 runs over 17 miles - including the marathon I paced in 4.45.
Last long run was ave pace 7.05 overall with last 4 miles something like 6.15 - 6.45 pace. Course was undulating hence the big range.
Usually I can pick up the pace to MP (2.50 pace) + 5-10 seconds in the last 3rd or last half of long run without falling to my knees at the end.