Stihl PMX 3/8 .050 lo pro ripping chain. Regarded by many to be the best lo pro ripping chain. Expensive due to the time consuming and awkward method of sourcing but now available from chainsawbars.co.uk.
This runs superbly on the specially built GB lo pro single piece steel bars to give exceptionally fast clean milling. If you can this is the set up you should be using for cutting timber.