tab, i'm not a fan of iridium spark plugs, seen them fail more than once,
imo ford 071's
The 071 is certainly a tough cookie of a plug, but the difference on mine with IK is very noticeable, idle speed is slightly higher, just a lot crisper.
I've had many IK fail when setting my soft and hard cut limiters too low for noise, they certainly don't like a soaking and don't recover fully, not sure how the 071 would fare as never tried with these.
tabetha