I wish I was simulating the NH. Instead, we're a club layout that's not 100% based on reality, just in general on the Northeast/New England scene in the "transition era". That covers a lot of territory, but it's not exactly the NH in the 1960's (much as I might like it to be).
The FL9's are hardly unique. I have a number of brass locos that are much worse and are pitifully slow on DCC. For example, my brass Key Imports R-1 top speed is about 38 mph because the track voltage is about 14 volts, with the motor only getting about 12v. On DC layouts, you could crank out 19 volts easy if you had the right power supply. At that voltage, the Key R-1 runs fine with the 12v Mashima can it comes with. Also, a friend sold off all his brass F40PH's because they were too slow...same goes for the Kato F40PH's. The club had Athearn FP45's with Holland can motors installed. When we put in decoders, they couldn't get out of their own way. I had to repower them with Mashima cans.
Meanwhile, my NJ/CB L-1 can easily do 70 mph, which is kinda scary with a 2-10-2. It is almost as fast as my I-5's (which do 80mph).