I am taking the easy option I suppose and in the long term improving the engines breathing (exhaust and air intake) is the way to go as Kev has pointed out, but.........yes the old �ssss is one of the factors I've got to think of these days.
But yes for me I think it will work as I'm not a straight A-B person these days and like to take in the scenery. I will spend 95% of my time on the smaller A roads, B roads, tracks and off road so I wont be around the 5k revs in top much, if at all. Its just that 50mph / 3krpm point I want to improve if I can.
I'll bang it on and take it from there - its a quick job to refit the 15th if I'm not happy.Cheers guys.

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Work hard, rock hard, eat hard, sleep hard, grow big an wear glasses if you need em.