You probably already know this stuff, but I thought it might be useful to somebody..
BPR6EGP is the Platinum plug, a BPR6EY would be the Vpower.
I wouldn't spend the extra dollars for Gold or platinum if you aren't fouling them with the water injection going. We ran platinum plugs to reduce fouling in 2-strokes primarily.
A six is considered to be a pretty hot plug in most circles. Our Slants run 4' and 5's in stock trim. With the higher compression engine, and higher head temperatures that are found in highly modified engines, along with improved mixture control, running that hot a plug may not be necessary.
The heat range tells us how well the plug's central core will dissapate heat. If you look at a 4 heat range plug's ceramic, it doesn't contact the threaded grounding surface until deep inside the plug. A 9 or 10 heat range plug has the ceramic bonding to the plugs threaded section much earlier. Conduction is higher, so the core of the plug sheds heat more quickly.
The spark plug can be a source of detonation if the sharp edges retain too much heat. It is generally such a small surface that this doesn't come into play.
If you can run without the projected electrode, I'd try something in a B8ES just to see if it works and doesn't foul. It should be quite a bit less expensive. This plug is not a projected electrode, nor does it have radio interference resistance built into it.
For NGK, E is the long reach thread, and an H is the short reach thread.
With the standard plug you can readily pick up B10ES plugs. They are used in high performance two stroke MC engines, or should I say "Were when I was in the industry." Does anybody run two cycles anymore?
I've run V-Power plugs to good effect in many of my sixes and eights. I was running the GR4's in the Valiant until I went to the projected electrode plugs last change. I can't say that the projected electrode plug works any better than the V-Power did, 'Cause I broke another of my rules; "Don't change more than one thing at a time!"
CJ