You asked for unbiased opinions, but I'll chime in anyway.
I think you have it bassackwards with the 270º vs the 360º motors. The 270º is the preferred motor for the flat-track racers due to it's quicker response and torque ratings. I don't know all the high tech specifics of it but I have spoken with Bill Gately at Bonneville Performance and this seems to be the opinion of the serious racers that run our bikes.
All that said, I would stick with the 270º motor and toss in a big bore kit with upgraded valves as well. There are several kits out there now and the differences are what will make your mind up. There is the Wiseco that I use, has steel sleeves that samo say are not as long lasting as the others that bore and re-coat the cylinders with nickaseal (sp?). The issue I see there is that the cylinder walls are thinner and more prone to breaking under severe conditions. But I may just be speaking out of my arse on that part. I know mine has about 30k on the wiseco and going strong. But I have also known one to blow up, one to have to re-ring and now another that tells me he is using a little oil with many thousands of miles. I dunno, your choice, do the research and talk with actual users of the various kits, not just the sales guys. Real results are what you want.l
Also I believe the wiseco kit gives you a 10.5:1 compression rate as well, I run mid grade gas as regular here in the tundra has 10% ethenol and the regular can ping or chatter a bit if I get gas at one of the cheaper stations. 89 octane is no problem though and I think premium is a waste of money, dyno'd both with no difference.
