I've run both the Denso IT-20s and the Brisk plugs, which are in the truck now. I picked up 14 RWHP on a Mustang dyno with the Brisks and charted the pulls for Mark Silvestri at LFP. Both plugs work really well and provide excellent longevity. The biggest difference is that the iridium tipped Densos don't like nitrous, whereas the Brisk plugs handle it just fine.
I also have o.e plugs with 18k miles but I have also been having engine troubles that my dealer cant seem to fix. They replaced a couple coil packs but still runs at about 2000 rpm with a skip like feeling! Not sure if it is spark or fuel. Seems like something they would be able to fix. It also set the check engine light once. Any hel pwould be app.