I stop sanding at 150, and yeah, maple's a bitch. I use a spray/wipe/spray process where I flood the piece, wait 60 seconds, then wipe all the excess away and let dry. The second spray is a light coat for colour.

Hate to say it, but I would strip the rail completely, sand 80 - 120 - 150 then re-stain. While I don't usually use a conditioner, that particular piece of wood might call for it..