2:41 at Sun City Marathon, 80 degrees at finish and net uphill course
2:50 at Boston, seven years after PR. In between had cerebral malaria and a couple weeks in intensive care.. and didn't race at Boston.
I was in about 2:45-48 shape for Boston I think, based on the 10k 35:10 from 3 weeks before and 1:17 half in training. But wanted to 'have fun' and planned to run my first and only negative split marathon (out of about 60), duly did that. I had to ask the spectators for confirmation that we were past Heartbreak Hill, as I didn't notice it while running up..
raced Two Oceans in South Africa every year for well over a decade, 35 miles and mountains, so the Boston hills felt negligible.
Boston is a fast course, barring headwinds and/or freezing rain, and assuming your training has done due diligence for downhill running on tired legs.