DUBAI/LONDON (Reuters) - OPEC has delivered more than 90 percent of pledged oil output curbs in January, according to figures the exporter group uses to monitor its supply, making a strong start to implementation of its first production cut in eight years. Russia and 10 other non-OPEC countries agreed to cut half as much. Supply from the 11 OPEC members with production targets under the deal has fallen to 29.921 million bpd, according to the average assessments of the six secondary sources OPEC uses to monitor its output and which were seen by Reuters.