Hi Kenny.
I wish I had such an investment opportunity, I would certainly take it.
However I think your analysis of the numbers is incorrect. Using your figures, with that 10% rate of return, it looks like a 16 year break even. If you don't retire for another seven years, the IRA money would grow from 21K to 40,923. In the first year of retirement (year 8), you would earn $4092, and withdraw $6800, leaving $38215 in the IRA option.
The biggest thing affecting this analysis is the outsized rate of return you are figuring in. I know that a 10% rate of return can be had for a time, but definitely not risk free. The investment you would be buying is state government guaranteed.
I also had not heard about rolling IRA money into an employers defined benefit plan. Are you sure that this will be tax free?
Bryan