iridium is what they come with stock.

btw this would worry me about running the BRISK:

BRISK PREMIUM LGS - Type spark plugs are not suitable for underpowered (weak) ignition systems where cold start problems or high pressure spark blow-off can occur

They do make an iridium plug too, but there were no foot notes on them.

Interestingly enough the recommended plug for the GTP was the GOR15LGS with up to +50 additional HP, but the GO14IR (iridium) was recommended for stock +100HP.