A 0.8 gap will be plenty enough spark. With the larger gap you run the risk of blowing the spark out, or not having a strong enough coil pack to power across the gap. If the larger gap works, then thats fine, but nothing wrong with running a slightly smaller gap
Splitfires are replicas of OEM's, well of course they are, there would be no point making them different so you hav to mod your car to fit them. OEM's are fine, If you can get brand new ones, buy second hand ones and you could end up buying coilpacks on the way out and have to buy another coilpack or set.
I've run Splitfires with 0.8 gapped copper spark plugs for the last 2 and a bit years, never ever had a miss running 18psi all day every day for the last year