I'd expect the BPE's to have substancially slower twists than a NE. This is due to the light-for-calibre black powder bullets compared to normal heavier for calibre nitro-express loads.
Seems to me I read the .450NE had somewhere around an 18" to 20" twist to stabilitze it's 480gr. bullet.
The .450 BPE normal 1890's factory loaded bullets ran 270gr. and had a twist-rate of between 40" and 60". The quicker of the two twists might stabilize a bullet up to about 360gr. weight, which was used by some African hunters.