Quick update.
I sold the 5K today to SLO-030 to make way for something with a little more potential from the Mazda stable.
Thanks to Kangaroosa, I've also decided to head down the Rotary path, with something along the lines of a 12A Extend Port setup.
I have a lot of reading on Rotary engines to do over the next few months to get a better understanding, but from what I experienced from a near stock motor (correct me if I'm wrong Darren), I think its the most cost effective way to go and also a way to go that I can get it engineered easily enough.