first of all, sorry for my bad english
Normally I only speak two languages, german and bad german...
sorry, but what the hell is a "piggy back" ? Do you know another word for it ?
to the topic...
I would say, that a rev-limiter at 7250 rpm ist the limit to keep the engine and all important parts healthy.
Maybe 7500 would be possible, but I would not recommend to drive these Revs for a long distance. The "Hydrostößel" ( the Things that adjust the "gap" between the camshaft and the valves ) only survive Revs under 7500, and even Revs below 7500 could hurt these "Hydro Stößel", if you drive it for a long time.
In my opinion you should get used to this rev limit. To raise the limit could mean that your engine looses some Reliability/Durability.
Like I said, maybe 7400... but not more.
Also the bearings are often responsible for engine damages of the x14xe/x16xe series. Maybe this should give you some thoughts...
I think the curve of the diagram is quite flat at its ending. I would leave the rev limiter where it is... I think there isnt much more potential that you could set free by raising the limiter...
Hope I could help you...
Good Luck with your engine ( nice Data by the way ),
and Merry Christmas