You can legally log it as per the FARs, but the above is a valid point. I had a friend get shot down in an interview because he didn't sign the log book as Captain, but legally logged PIC as per the FARs.
If you can legally sign for the A/C as PIC for the Part 91 flying, reposition, deadhead, etc., then I would tend to log the PIC time. Most interviews don't care what was in the back of the plane or the type of flying. Soon you will have the ATP and it won't be an issue. When you have 5000 hours for the interview, nobody is going to give two sh!ts about a couple hundred hours of part 91 PIC.
A little story:
An airline Captain/mentor questioned me about 6 hours I logged as PIC while acting as a safety pilot in a C172. I thought about it and asked if he logged the time while at crew rest in a first class seat on the B767? If there was a column to keep track of the Gadiva chocolates he took from the credenza while watching the movie?
Do what you think is best, but always have an FAR to back it up.
About the safety pilot time, I had one of the top FAA-guys in charge of FARs on the JS out of DCA and ran the scenario past him and he said I had logged it legally, but again, I guess I had better take out those six hours for the big airline interview!