Hi
I normally shoot a straight stock Remy 1187 for practical (as we call it in the UK), but went over to 'limited' pump for the European Championships this year. My gun was an 870 with a pistol grip, but half way through the year I took the p/grip off and put a straight stock on, and never looked back.
I found that with all the 'spinning' of the gun for the reloads the pistol grip just got in the way, and as I find no other advantage to the pistol grip thats enough to put me off. I actually do less spinning since I came back having picked up other ways of doing the same thing (Thanks Kurt!!) but have kept the straight stock.
At work (Police) our shoulder weapons are mainly the H&K family which are all pistol grip, but as with them it is just 'mag out, mag in' I don't even notice. Our shotguns are only used for 'doors and dogs' with other roles covered by rifle/carbines.
Kurt, you're right, when 'push comes to shove' you need both hands and all your concentration for the threat, however (thank the lord) that happens very infrequently and there are plenty of times and needs to do both!
Cheers