you may find that your missfire is caused by the 1.1mm gap. If you were to put 0.8mm gapped plugs in there, the problem might well be solved.
if you can run a 1.1 gap on the new coils without missfire, that's ideal. generally, the larger gap you can maintain, the better the combustion. ie, bigger bang.
if you need to run 0.8 to avoid missfire, thats fine, and very common. going lower than that is generally something to avoid.