Differences Between Polar Express 2-8-4 Berkshires

Hello all -

I'm trying to determine which Polar Express Berkshire to put on my to-get list:

6-18754 Polar Express 2-8-4 Berkshire #1225 with Whistle Steam (~$265)

OR

6-31960 Polar Express 2-8-4 Berkshire #1225 loco and tender from RTR set (~$110)

I don't mind paying for the 6-18754, but ONLY if it will net me some additional pulling power--I don't care about steam chuffing, railsounds, the die-cast tender, or any of those miscellaneous extras.  Are the engines of these two locomotives mechanically identical, or is there a power advantage in the 6-18754?  Forgive me if this has been covered before.

6-18754 Polar Express 2-8-4 Berkshire #1225 with Whistle Steam

•Transformer controlled forward, neutral, and reverse operation

•RailSounds RTR sound system with steam chuffing, steam whistle, bell, and user-activated crew dialog scenarios

•Operating headlight

•Puffing smoke from main smoke stack

•Whistle Steam effect

•Operating coupler on rear of tender

•Powerful maintenance-free motor with momentum flywheel

•Traction tires

•Die-cast metal locomotive body and trucks

•Die-cast metal tender body and trucks with metal frame

•Engineer and fireman figures

6-31960 Polar Express 2-8-4 Berkshire #1225

•Transformer controlled forward, neutral and reverse operation

•Air whistle in tender

•Operating headlight

•Operating coupler on rear of tender

•Powerful maintenance-free motor

•Two traction tires

•Puffing smoke

•Die-cast metal locomotive body and frame

•Separately applied metal handrails

•Large pilot and headlight lens shield