I'm wondering how the new blended retirement system chages the math.
Easy
Ignore the 1% base pay match. It's a meaningless drop in the bucket, likely worth less than $100K after 20 years, depending on market performance.
The new pension is 40% at 20y instead of 50%.
A reasonable way to put an instant cash value on the pension is to get a quote for an inflation indexed single premium immediate annuity.
Presently a retiring O5@20 gets about $52K per year, and assuming he's in his mid-40s a SPIA for the same cash benefit can be had for around $1.25 million.
The new system's pension "cash value" is probably worth about $1M (+health ins benefits which are hard to quantify).
So under the new system if you're at 12y and need to spend an extra 8 to get the pension, you should consider that during those 8 years the military is effectively contributing about $1M/8 = $125K/year of pretax dollars to your retirement in addition to your paycheck.
During those 8 extra years on AD, if you're making $200K/yr with a RP (aka MSP) contract, add the $125K to get a rough estimate of your total real compensation ($325K) ... which ignores tax benefits, which aren't trivial.
Now consider that as a civilian you can't easily put away $125K/yr pretax ... the equivalent civilian salary to match the military pay and retirement saving is probably $375K W-2 or $425K 1099.
If you can make more than that as a civilian, then it makes financial sense to get it at 12.
If you've got 15 years in already ... then the pension factor is $1M/5 = $200K/year and now your effective .mil pay is around $400K and the break-even civilian pay is pushing $500K.
If you're at 17 years, $1M/3 = $333K and break-even civilian pay is $650K+. It's almost always bad finance to get out that late. But money isn't everything.