From my experience, north easterly departures from MAN are mostly obstacle limiting (Stockport, Saddleworth Moor, Pennines etc.). Both rwys are close to one another, so a general assumption that they are affected by the same obstacles holds true.
However, their two thresholds are significantly displaced with 06R being the further to the west. This puts 06R further away from the obstacles, ergo better take performance & less limiting on weight.