Before moving over to 4x5 film, all my still life subjects were taken on digital using just the modelling lamp inside a soft-box and an occasional grid. Just by adjusting the ISO / Shutter speed, I could more or less get the low key effect I was aiming for right out of camera.

4x5 Film is a different ball game
Apart from not been able to see the exposure ( I don't own a polaroid back) I am finding that the negatives are not quite producing what I want. To give you an example, at f/32 the light meter is reading in the region of 15 - 30 seconds when using the soft-box. At these long exposure times, I am running into reciprocity which is also another headache.

Rather than try to get the low key effect out of the camera, on film, would I be better creating an average exposure (increasing the light intensity) and then trying to re-create the low key effect in post production through dodging and burning ?