You do not want to be in OD unless you have really have that trans built to go there.. Very few are set to handle big power in OD. Plus the drop to
Drop to a 28 in tall tire. Cheaper to test that set up for RPM. what is max RPM on the engine? A few links with gear calc programs . A 30 inch tall tire in bias or radial?? Tire growth will come into play with a bais tire if that is what you have now, my dealings has been that tire is growing at least 1-1.5 inchs on the big end
Try this one..
http://hotrodworks.net/hotrodmath/quarter.html
http://www.locost7.info/gearcalc.php