Low Wines % effect on spirit run

[higgins]

What kind of difference should I expect in a whiskey spirit run with 6 gallons of low wines at 31% instead of just under 5 gallons @ 40%?

I've got 8 spirit runs under my belt now, and I've always run my low wines at 38-40%.
I've got a bit under 5 gallons of low wines at 40%. I'd like to increase the quantity a bit to ensure that I won't dry fire my element, and diluting to 6 gallons would do that.

Will the run go any differently than what I'm used to?

I read where some folks add a bit of the backset to the spirit run with the idea that it will help carry more flavor over into the final product. Does this really work? what amount would you use?