When you say one piece sear, is this what you are talking about?
http://www.ericgrauffelonlineshop.com/en/frame-parts/348-sear-lever.html
Honestly, the best result for the SA pull, has come from filing the hammer hooks and the bottom of the sear lever. Its not perfect, but a whole lot better than before. I notice on mine, in double action, that the hammer/sear lever contact has the biggest impact on the gritty feeling. If you take the sear assembly out and work the trigger, the plunger "at elast on mine" doesn't provide a whole lot of resistance.