If they ever do bring Amtrak service along that line how fast would it go? I know it wouldn't go nearly as fast as it does now along the Boston-Portland route.[/quote]
That's a mighty BIG if. Right now the only plan for extending regular passenger service north of Portland is to rehab a long dis-used freight spur in Portland towards the waterfront area, build a brand new bridge over to the St Lawrence and Atlantic at East Deering, and use it to go to Auburn, by-passing Guilford. There is also hope of running trains to Rockland via Yarmouth Jct on the SLR to the current ST Brunswick Branch( a connecting track would have to be built). The project is slated for completion around 2007, I think.
If passenger service resumed on the old MEC, I'd guess the mainline would get an overhaul similar to the one the Freight Main got south of Portland, meaning 60 mph maximum, if not more.