The efficiency of the Ivy Bridge chips is giving a tough time to the processors from the 2011 slot from the prior generation.
There is to be a new sort of 2011 processor sooner or later whereas there is to be no more new 1155 processors, so that could make a difference.
Anyway, the 2011s used to be king of the hill and that is why they costed so much. They are still the king of the hill if you get the $1000 processors, but the cheaper ones are beaten $ for $ by Ivy Bridge I am pretty sure.
Anyway, my vote would be for the 1155 unless you have many many hundreds to drop on the processor alone. Not just 2, I am talking like 5+.
I would mostly ignore the concept of future proofing, it doesn't work and even when it does it isn't cost effective.