There are many good plugs to chose from. If you plan on running 30% fuel you'll want to stick with a COLD plug. I normally run the McCoy MC-9.
There are also alot of good pipes on the market that will work well with that engine. One that makes more power than most with the P5X is the MSR 1005 but it's not cheap. It's also a little soft and dents fairly easy if you get punted on that side. The 053/9853 is also a popular pipe for that engine.