This is a tricky bit of road, mostly because of the potholes. I couldn't say, however, that motorcycles have made me feel less secure. I'd say that having motorcycles in the bus lane north of Brixton is an advantage - by far the greatest risk (apart from my own stupidity) is from cars turning across the bus lane, and motorcycles act as a deterrent.
I think you'd be daft to go to the left side of the lane. I'd settle for about five foot from the kerb - this is how Mrs L goes down the hill, and she's not fast.
Have you thought of using Lyham Road - taking it all the way down to Kings Avenue, then going on to Clapham North? It has speed bumps, but if you're not travelling quickly that's not a problem. It's not as steep as Brixton Hill, which makes the southbound trip easier.
Kings Avenue now has central islands, creating pinch points. Lyham Road avoids the worst of these.