Here is the link, http://www.opm.gov/fers_election/ri_90/f_bbp.htm
You might want to look at the link above. "Do I understand you to state that Fed Pensions don't use some kind of Acutary based sliding scale?" No, the FED pension is ok. It's more of an issue of when you can collect the benefits and if you will have to take a reduction. If you hit 30 or more years, there is no reduction to your pension, you can collect at the MRA and receive the SS supplement. With 29.9 years or less, you will have to take a reduced pension if you retire at the MRA (and then collect the SS supplement at age 60). With 29.9-20 years of service, you can wait until age 60 to retire and not have a reduced pension and collect the ss supplement at the same time.
If you leave service before age 60 (whether or not you retire) your pension is eroded by inflation. My 43% number was based on a reduction in the pension by inflation, taking the pension at the MRA with the reduction, a small reduction in the SS supplement from not adding SS credits which effects the SS supplement, and not adding years of service to the calculation. My 17% number was based on the effects of inflation to age 60, not adding years of service to the calculation, and a very slight reduction in the SS supplement. I took the numbers based on the benefits received at age 60 because this benefit age made the most sense to me.
Hopefully that helped.
Kind Regards to all,