Have done a +4 on Provia 400X, you're only supposed to increase FD time, but I also increased second bath (wash time), the bath responsible for lifting up shadows, this lowers contrast back down from being excessive, and it works well, though needs to be carefully balanced so your dMax isn't too thin from that combination of +4 and more time in 2nd bath.
Originally Posted by Hatchetman
This is what I use (with timings for 1/3rd stops)
6 minutes for N
9 minutes for +1
12min 20s for +2
15min 26s for +3
18 minutes for +4
I think its too late to fiddle with these, esp increasing 2nd bath time when planning on projecting.. you need to try a still test roll first.