i think a range hotter would help. I run H12 ( 512 ) in my machines.. and actually.. mostly I've switched over to autolite 437 thought the 216 xref from the h10 works too..
changing plugs 2x or yearly? OUCH! do you have an air compressor? if so, for the price of 1 set of plugs, get to harbor freight and buy a abrasive plug cleaner.. lil softball sized job that has an air hookup and a push button.. has a lil bag you fill with black beauty abrasive ( included ).. and a rubberized hole to stick plugs in. takes a 15-20 second shot of air as you agitate the device to get the abrasive moving around. I've had one 5-6 ys and still on the abrasive that came with it.
have a cloth to wipe the plug threads down, and a can of carb spray with a stray to spray clean the abrasive that makes it up by the inner electrode.. DO clean it all out or it will wear the engine.. once clean.. regap and go. I clean all my plugs now.. I keep a bucket in the garage.. when I pull a set I toss em inthe bucket.. when the bucket is full, I take 10 minutes and clean em all, and repackage them back in their lil boxes that I have saved over the years. I always have a a few clean sets on the shelf when needed to do swaps, so i'm not tied up cleaning a set on demand. probably have oh.. i dunno.. maybee 10 sets of plugs for various machines in boxes, cleaned and gapped and ready to go... havn't bought a new plug in years. did get lucky about 5-6ys ago and when tsc dropped champion to switch to autolite, I bought the metal champion display case.. actually got the case/dispenser for free.. manager told me if I bought al the plugs in it I could have it. must have had 38 plugs in it.. I got them for 50 cents each clearance.. so 19$ for all them plugs and a wall display case!! cleaned plugs have a marker cross mark ont he box, new ones don't.. thus I know if I am pulling a cleaned or new set off the shelf.