I know there are rotaries in Australia that run in the 7's over the quarter mile (from engines making 1000+ hp), so the fastest would probably run high sixes maybe? Advantage of Rotaries is they're physically smaller and lighter, with fewer moving parts, and generally make more power, than a piston engine of equivalent displacement.
I wouldn't, however, suggest that rotaries are more suited to drag racing than piston engines. The fastest piston engined quarter miles are in the sub-4.5 second range (from engines making 8000+hp). Piston engines have had more development over history and are therefore more suited than rotaries for most applications, whether it be drift, drag, economy, towing, etc. There's simply more time, more money and more experience being put into piston engine development than rotary engine development. A rotary will never be the most economical, most powerful, or most reliable choice for an engine. When rotaries have more than one manufacturer doing the development, maybe we'll see increased competitiveness.
When it comes down to it, people like rotary engines because they're DIFFERENT, not because they're the ideal engine choice.