question for the contractors out there, R11 vs R13 insulation

[keakar]

how much real difference is there between R11 and R13 insulation.

I have a chance to get a bundle of R11 insulation at half price and wanted to know could you really tell the difference or would it be such a small difference as to not be noticeable?

guy was told he bought the wrong kind so he went buy R13 and now is trying to sell the R11 for half what he paid for it.

they are both 3 1/2" thick x 15" bats so im thinking I might use it in my house unless its going to make a lot of difference just for those 2 digits of R value.

from what I have been able to tell, R11 is mainly used in basements

house exterior has 5/8" plywood on top of house wrap, then 1/2" sheetrock will be going on after the insulation

should I buy it and not think twice about it or pass and get R13 because it makes enough of a difference