Saphan Kwai is now just a nice memory. Only "Charming" bar (if you like to pick from bored looking college boys sitting facing you.) They just want to pay their way through school, but you can meet some nice horny "amateurs" there.
In Silom I'd still start with Screw Boy as the most fun and flirty bar...its worth going to see the 2 go go boys thrashing around in front of the shufflers. Last time I was there they let a twinky, but slightly podgy farang strip down to his jocks and join the boys on the stage. He thought he was hot, but compared to the Thai boys, "white men can't dance" was never truer!
So after a couple of days in BKK...why not head here to Pattaya for some real fun??