By Marcy Nicholson and Sarah McFarlane Reuters via FOREXYARD August 19, 2010 NEW YORK/LONDON, Aug 19 (Reuters) - Arabica coffee futures finished firm on Thursday on position rolling and roaster nibbling ahead of September's first notice day next week, but shied away from the recent 12-2/3-year top. Sugar and cocoa futures finished mixed in quiet dealings. Arabica coffee dealings were choppy as market players rolled positions out of the September contract, ahead of its first notice day Monday, into December, while roasters and investors bought the dips, dealers said. The move lifted the arbitrage of arabica beans over robusta to $1 for the second time this week. Arabica futures have soared more than 30 percent since mid-June to a 12-2/3-year high at $1.8290 per lb on Aug. 16, in a fund-led rally. Prior to the rally, the arbitrage ranged from about 71 cents to 78 cents. "The market is a bit tired up here. The market's signaling that it may not be able to sustai...