Does anyboy use tesco 99 ron in a 'classic' sti?

Was reading an australian site on ethanol blended fuels that said subaru state e10 (10% ethanol) was unsuitable for 1999 and 2000 impreza sti models.
I know the tesco stuff is only 5%, but was just wondering whether there were any incompatabilities with ethanol in the fuel system, oxygenated fuels or just because the e10 sold there is lower octane?

Thanks.