I always went heavier than that. I use an olde Manfrotto/Bogen 3050 (or maybe it is a 3051). Bigger is better -- the Cambo monorails with long rails are heavy and unweildy. I find a big and heavy tripod tames the camera better, especially when used indoors in a studio to take portraits as the OP intends... or near the car trunk when taken into the field.
Good to know! I've toyed with the idea of acquiring an inexpensive 4x5 view camera from time to time, and had assumed that the Tiltall would be adequate. Thanks for the info!