Sounds like you do exactly what I do. When I'm due for a "clean" I drive in 2nd (auto) at full throttle @ 5500-6500 for as long as I can up the steepest hill I can find and then use the engine braking to slow down again (also using 1st when the speed's low enough). I've found this really heaps keep the engine running wels as well as sounding great.

As for the blowby, I thought blowby was when the oil got into the combustion chamber during normal driving (except WOT).

My best example of blowby is in my '76 244Dl with 700,000kms. when you hold it in 1st (auto) and take it to 6000rpm and then close the throttle, it blows HEAPS of smoke and then when I floor it again it blows even more smoke (I seem to have developed a habit of blowing smoke when ever there's a f*$% W*@#^! tail gating me......they don't come close to me again :)