Is there any benefit to boiling with less water than your final amount? I have done 6 gallon boils for about a 5 gallon fermentation. Any reason to change?
I think the less you have to top off, the better. Everything I've read is that full volume boils are better than partials. If you got the room and the BTUs, full volume it all the way!
Full volume boil is usually your best bet. You will get better go utilization the more water you boil with. Also if you boil with less water the wort may darken some and form more melenoidens.
The main advantages of partial boil are smaller kettle needed, less gas or electrical required for the boil, and much easier to chill (can be chilled in an ice/water bath). Late extract addition can minimize wort darkening and provide good hop utilization. But assuming you're getting a good boil, partial boil wouldn't improve your beer quality.