Great analysis and I agree completely with the likely outcome, if we had been allowed to engage the North Vietnamese when they broke their word and the peace treaty. As you point out Kerry and Murtha would like to repeat this betrayal in the WOT. That's one reason I agree with Democrats when they say that "Iraq is Vietnam all over again," but then I have to explain to them that the left's "victory" over Nixon in Vietnam was not some glorious thing but was one of the lowest points in the history of western civilization.
There will be a serious reexamination of the entire "peace movement" and the history of the Vietnam war someday that will absolutely eviscerate these people. Kerry, Fonda and friends will be spat on every time they go out in public.
BTW, in 1975, our first A-10s and F-15s were being delivered to the combat wings. Imagine them over the concentrated columns of armor of the North Vietnamese forces! F-15s on top flying CAP against MIGs, with A-10s raking T-72s and BMPs with 20MM depleted shells from their Volkswagen-sized gatling guns!