Ross, Are you 100% it's a ping? I run BCP7ES plugs, there a heat range colder than the 6's, gapped to 0.7mm. Stock pump could be going, but you'd expect it to happen under full-load. Might be worth getting injetors flow-tested. Blow-by is more likely to happen at high-rpm.
I'd get it on a dyno, and make sure that it is a ping, then look at the AFR's there the most likely indicators:D