RE: Too tite?
What I have found is that .660 shoots a good Lead/Copper load. The thing is that .660 and .665 are not all that much different. Its a very small change and from what I seen they are very close. If your ever planning on shooting heavy shot make sure the choke you decide on is Heavy shot compatable. You can still shoot lead out of thst choke, its not the sizing difference but rather the quality of metal in the choke that changes.
As far as a distorted pattern that has more to do with the forcing cone in the gun you'll be using. The new turkey guns tend to have a longer forcing cone allowing for a more even look to the pattern.
I have seen 3 inch shells time and time again shoot tighter then 3.5 shells, so don't be scared to try out 3inch...