Besides a train with 4 Dash-9s and 15 COFCs the only other trains that I've been able to reach the summit with are the Flying Scotsman w/ 4 cars and the UK's Class 50 w/10 cars. I have a very early demo version with only Microsoft add ons. I think one can also reach the top with SD40-2, 2 gons and a caboose. Once you reach the loop track one can slingshot right back down the hill. I go downhill through Essex at usually 135mph with the Scotsman and hit between 194-199 mph at Pinaccle. No derailments or wrecks unless I throw a stub track switch. I am also able to go on to Shelby if I have the time. Trains some times come apart at Cutbank, but they can be recoupled and finish the run.
sincerely,
sffoamer
Getting MSTS Bin from http://mstsbin.uktrainsim.com/eng/eng.html should help, as well as add a lot of interesting new features to MSTS.
Also, getting Marais 3.1 will help alot since the 5% grade on the original is not realistic at all.