Yeah, I had to look it up. The C63CX is the hottest in that style. If you can find them, you can get a C63 which is one range hotter, but it's a fine wire plug with the standard ground wire. The C65YC is the same heat range as the C63 and is one range hotter than that C63CX you are using. So the C63 and the C65YC are the same heat range, with different tip styles. BTW, the C65YC is an extended tip, which IMO is better for pump gas stuff.

I used to remember this stuff off the top of my head. Tonight I had to get the book out! Sucks getting old.