Are you on MTP? To find the best settings I would start without OC and run default intensity. As soon as the hashrate is stable I would increase intensity. Repeat that until you do not see higher hashrates. Then use the best intensity. After that you can play with some OC and see if that have any impact to your system. Sorry that I do not have a more 'concrete' advice, but systems are too different to give general hints that fits all of them.