Brett.. my circuit will generate such a weak spark after 10,000 rpm that it seems to just quit, touch the spark gap if you don't believe me.. it'll still bite ya!
The cap recovery time is too slow after that speed.. Since I never intended to go beyond that range it never bothered me.. I used to run it on a tired old K&B .40 engine that ran up to 11,500 but the spark on a NGK-ME-8 gap of only .20 still let it fire...so it kept right on running. A larger gapped plug would have just quit. I then started running only weedeater motors on ignition and haven't had a problem with them at up to 8,500 rpms..
You could drop the .47 to about .33 and still get performance levels you need at higher rpms though. I have tested that value and it did work. Without anything but a crappy VOM here I trusted my eyes and ears for the spark. Everyone seems to have correct solutions though and I agree with them all..

John