Parmer,
Congratulations on the 80% rating! This link here
Compensation Rate Table - Effective 12/1/08 (U.S. Department of Veterans Affairs)
shows the current benifits rates based on your rating and also whether you are single, married, have kids, etc. As a 20 year retiree, your VA rating should progressively become concurrent to your regular retirement. I think DOD has been phasing it in so that you can receive all of your retirement, and also your VA rated pay at the same time. It started in something like 2004 with 10% of your VA benifits being concurrent to your retirement, and then goes up each year by 10%. So right now, all things being equal, you should see something in the neighborhood of 50% of your VA rating benifits plus all of your regular retirement. If I understand it right, most everyone agreed it was crap to take away, dollar for dollar, your retirment in order to get VA pay, but it amounted to ALOT of money for the GOV to come up with, so they are "phasing it in" over time.
Lemme preach on it:
If your regular retirement right now is $2000 (just an example) and you are rated at 80%, assuming you have no kids and no spouse (and no parent living with you), you could stand to see $1427 from the VA. I THINK the concurrent rate is 50% (somebody correct me here), which means you would get $2000 in regular retirement and about $713 from the VA in pay ($2713 total) of which only $563 is actually now taxable.
Look at the charts and figure out your rating for your situation,...add roughly half of that to your regular retirement, and you have your pay. Subtract ALL of that VA benifit rate from your regular retirement and you have the amount of TAXABLE income.
Ok, bout to get a nose bleed here. If I am way off, somebody smack me. I hope this helps more than it confuses!
Pretty good review of the CDRP right here as well
http://www.military.com/benefits/military-pay/retired-pay/retired-concurrent-receipt-overview