Andy the service rating of the motor is about 8800 RPM at -maybe- 14V. This works out to about two feet per second actual speed. You can time it... if one "lap" of your mainline is, say, 20 feet, then 10 laps should take around 100 seconds at full speed. If it's much slower than that, you could try removing the die-cast boiler shell, and putting one DROP of Labelle 107 on each end of the motor shaft, where it protrudes from each end of the "can."
There might be a tiny voltage decrease through the circuit boards, but personally I wouldn't exceed 16 volts on the track. A 1033 should be plenty for this loco. If you're not happy with how it runs, then I suggest you resell it. Because you cleaned it up cosmetically, you might get more than you paid. There are PLENTY of RailKings and traditional-sized Lionel steam that would fall somewhere between this and your MPC in terms of speed.
