Peak breech pressure isn't the only concern. It's the pressure wave - it's time length and development of pressure farther up the barrel than when BP is used.

I find it difficult to believe you could safely duplicate Nitro Express loads in a BPE and come out smiling.

There is just too much difference between 1,800fps and 360gr. bullets and 2,100fps and 480gr. bullets.

Pressure wise, the odd gun might handle it - is it worth the risk to find out your's won't?