There's a fellow named Dutch Schoultz who's developed a very successful method for determining the optimum load for a black powder rifle. His web site is http://www.blackpowderrifleaccuracy.com/
He sells a set of documents that describe how the method works for $20; it's the best $20 I've ever spent on black powder in 40 years. Dutch is in his 80's now and lives on social security and sales of this system. He's a great fellow, very interesting to talk to on the phone.
The system doesn't address sabots per se but the method will give you a great deal of insight into how to go about accounting for all the variables. It would be well worth your time and money.