Have tried a couple of RTV's, including a 1:1 mix. Best one I have found is the one Lurecraft is selling...mixes well, cures well, holds up well, price is not terrible. Don't get to confused on mixing, mostly 10:1. Just get an oral syringe from a pharmacy (kid's dose syringe), will give plenty of accuracy for drawing up the catalyst. Can measure the RTV base in pyrex with good accuracy.
I have used RTV and hardener with, and without color (the blue stuff). I think it is a little easier to mix and make correctly with the color additive, lets you know when your mix is well blended.
The clay I have the best results with is Van Aken Modeling Clay (Michaels, Hobby Lobby, etc). It never hardens, shapes well, and is heavy enough to hold well to the botom of the mold container. Listed specifically on the packaging as compatible with silicone mold compounds. No mold release necessary. It is the clay I used to proto the drop shot baits I have posted in the gallery...went from proto straight to the first RTV mold.
www.vanaken.com
Hope it helps.