I too understand your delema, I gave in to my RC want and got the BD and am currently running it. I never owned a belt drive except for the Yokomo Mini TC (which is for sale) I have been condenplating on selling the SD/Rayspeed because I don't have time to run and maintain two cars. I am going to get a good final setup on both cars and then do lap time tests and which ever gives me the most consistant lap times will be the car I will keep. Right now I am being very consistant with the BD it is different to drive that is for sure. I was going to get the LCG conversion but I dought it will make me any faster and being that it will cost more than $200 it would be really hard to explain that cost to my wife.
I think if the SD is your winner car right now than the LCG is right for you. But with a new chassis it would put all the expence of the Rayspeed upgrade in the trash.
Just my thoughts....
Stephen <><