I would not go from a 2011 to 1155 because the 1155 is due to be phased out. The new Ivy Bridge-E 2011 was going to come out this year which would make the old Ivy Bridge CPUs out dated. It would be cheaper for you to upgrade with in your current MoBos socket and wait for the new realeases that are due at the end of the year than it would be to get a new MoBo and CPU.
There is also rumor that the next Tock chip might be out this year, the Haswell 1150 chips which would require a new MoBo and probably RAM. So if you went back to a 1155 you would end up having to by a new MoBo when the Haswells come out.
As for bang for the buck. Like said above it all depends on what you are doing. If you are using it for games then most games do not take advantage of multi-core CPUs and get most benifits from a good GPU graphics card. If it is rendering however then CPU is important. If you are over clocking then you will need an Unlocked CPU (ones that end with letters like K and X). If it was me I would go with a 3930K. It is a decent price around $500 and has the ability to do most of what you want.