I'd also probably opt to not broil them but, as rotus said, maybe you can try one that way and see how it turns out. I'd be more likely to bring the steaks to room temp, preheat my B to the desired internal temperature (or just below), then cook the steaks until done, followed by a very quick sear on each side in a very hot pan. (I have a rectangular cooling rack that, serendipitously, fit perfectly above the B's roasting tray. Just for the heck of it, I did a Google search for "Costco strip loin" (w/o the quotation marks), and found this pleasant and helpful video:
http://t.costco.ca/Kobe-Classic-Beef-–-10-Canadian-Wagyu-New-York-Strip-Loin-Steaks.product.100016464.html This is what I bought. As I said, they were only 3/4" thick. I did broil them, 4 minutes on each side which turned out to be medium. I should have gone with my inital instinct which was 4 minutes on one side and 3 on the other. Normally I cook steak sous vide and them torch them to brown but I wanted to see what the Breville would do with it. So now I know.