Steve, I replaced two 8 year old turbos, with only 400 hours each, in 2010 for the exact reason you mention above "too much area around the exhaust side blades allowing exhaust to escape without spinning the turbo", at least on the port turbo (the gap was huge compared to the SB side turbo) and then the SB turbo acted up only two months later so I replaced that as well.
Here's why I'm telling you this, my "new" port side turbo, with just over two years of hassle free use (less than 100 hours) is now just doing the same thing as before - rpm lag/bounce between the time the supercharger disengages and the turbo spools completely. This shouldn't be happening on a young under used turbo. I haven't had my mechanic pull off the exhaust yet to check the blades, but does anyone have any ideas as to why these engines are subject to this type of problem? Turbos are damn expensive to replace, I just hope some sort of warranty came with the turbo or volvo can replace for free if faulty?
Other than this, the engines are 10 years old, great condition and work great.
Mike