it will really depend on you, your size, your shooting dynamics, and the balance of your bow. If you are an average size guy, have a 28inch draw length and shooting a 38 ATA bow, I would say something around the 30" TO 34" should be great. You really need to set uop your stab to fit you, your dynamics and the bow. you will need to experiment with the weights, it is most common that most guys are running around 3oz on front and 7-8 on the back bar, butr that is just a general ave. and it is totally dependant on you.
give Blair (RIMax) a pm or bigGP, or BrownHornet they may have some good advise for you. or PM me with your info and I may be able to help.
good luck and great choice on the stabs, Harry