Hi.

Higher octane= slower burn rate of fuel, per combustion. Turbocharger=
higher compression ratio. Higher compression ratio= more explosive
combustion, which in turn = more power. Crappy gas= ping because it
doesn't combust evenly over the power stroke, sort of like a "flash in
the pan". Compound this effect with a higher compression, and you will
definately ping, and get worse fuel mileage, and possibly overheat your
turbo( the exhaust, which drives the turbo, from poor quality fuel is
hotter) which = more rebuilds/replacements,which=more$. Gas is pricey
these days, but not as bad as a turbo overhaul/replacement. P.S. The
worst gas you can get in Sweden is more or less equivilant to high test
here in the US.

Good luck, and keep her fed,
-Zeke-