Thanks for all the info guys, good stuff to get clear bulls**t free responses. Don't know about the GoPro video, don't look like he's running the thing too hard to me!
I have decided after much research to go with Eric Gore, so the cylinder is being packed up today and sent over. Hope this goes well..... am concerned about the upper O-Ring, and possible cooling issues, I do know the Athena cylinder has larger water jacket. Time will tell.
See my next subject about these Scalvini pipes.... just putting it together now, (the post). Looking at seriously conflicting tests about 4 months apart in MX Action magazine. One say on a SX 125/150 dyno test at 11,000 rpm they were up 7hp, as the standard pipe tapered off badly at 10,000rpm, now in this months mag, they have a YZ 250 in there, and this test they say the STANDARD pipe has a higher top end HP figure (I know that ain't all that important on a 250) but they really bag the pipes this time.
Oh yeah, happy new year all fellow KX riders!