What it appears to be, by my account, is a West German gun that has been modified.
The list on sigforums.com isn't complete by any means, but give a rough idea of where serial number dates should fall. Your serial number is in the range for a 1988 Sig P226, as well as your slide.
Herndon, VA was the home of SIGARMS from the late 80's to early 90's. So, your gun was imported through them in 1988. If your grips are original they should have a date stamp on the inside that looks like a clock that should match the guns '88 build date. You have a very nice looking West Germany P226.
You didn't say what caliber the gun is, but with the porting, I am going to assume 40 cal. Someone will correct me if I am wrong, but a ported barrel was not a factory option on your gun. Same goes for the nickel controls. I would guess that someone use to run the gun in open class competitions and had the slide modified and an aftermarket barrel put in.
Even though IMHO the gun isn't something "special", I bet it shoots great. I wish my Sig P226 looked as pretty as that one. Of course I don't have to worry much about adding yet another nick to the finish of my gun. Have fun with it and marvel at the flames coming out the ports when firing hot loads.