I should run 15% nitro
because of the altitude of the region (3500'). I can switch to 10% if that would be better.
That should be fine. Also the ST's sold here likely have a lower compression ratio than those sold in Israel, so I suspect it will work fine with 15%. Also try some differant plugs an Enya #4 or even #5 may help your midrange problem. High and low tank can also affect midrange, high tank rich midrange, low tank lean midrange.