The terms "reverse polarity" and "straight polarity" aren't used so much any more, but they're the equivalent of "electrode positive" and "electrode negative", respectively. The only electrode I'm aware of for which the preferred polarity is electrode negative (straight polarity) is 6012, and I almost never hear of anyone using that nowadays.
You're right that 6011 is generally run AC, and that's what it's intended for. Lincoln Electric lists the preferred polarity for their 6011 as AC, DC+, and DC-, in that order. Interestingly, they make one version of 6011 (Fleetweld 180) which appears to run cool. The suggested amperage for 1/8" is 60-120 AC, and 55-110 DC+ and DC-.