The A646 isn't so bad. For those who remember my return to bicycling, it's the third of the 'seven roads out of Tod, and six of them are up' that I managed (after the A646 east to Hebden Bridge (virtually flat) and the A-thingy to Littleborough and Hollingworth Lake. It's a fairly constant drag up from the Tod side, with a small drop before the last climb to the junction out of sight to the left of the photo. From Burnley, it's steeper in places, and plagued by idiot drivers, but shorter.
One of our number commutes over it on his recumbent.