I cycle daily to the City too. I avoid Rye Lane. I head down Crystal Palace Road, Ayds Road, Bellenden, Lyndhurst, Kelly Av, Chandler Way, Burgess Park, Portland Street, Falmouth Road (over New Kent Road) Harper Road, Great Suffolk and then Southwark Bridge Road and over the river. 25/30 mins to Cannon Street, and stopping at every red light!