I own the Slayer Extreme SE, Nitrous-X . I really love it for 3D and would highly recommend it for that. It however would not do as well as my Scepters on indoors.
The problem is the Slayer hold well and has very good speed, but it is not as forgiving and this is going to cost you a few points in the duration of indoors. Perhaps, you can handle it better than I can. I am not saying it couldn't do very well for indoors, it just takes a lot more concentration to get a good release everytime, etc.
I have been trying to decided on a possible replacement for the Scepter III's. But, I really haven't found anything which I truely think is better. I might look at the RazorX Magnum with Nitrous-X cams. I would try to get the biggest cam possible and use a mini-module on it. This produces the smoothest draw and possible generates a little more arrow speed.
As far as poundage, I would go with probably a 60 to 65# peak limbs. FITA events require less that 60 lbs. I would usually shoot indoors at about 50 lbs or less. Remeember, Martin's have a 15 lb. adjustment range and you can order about any peak you want.