(user deleted)

Great news David! It's incredible it allocates so much memory at the start of the session and later it runs just with 350mb or so with all sessions opened.

for the time being you can try trick the application to use more memory, running this neat tool against the executable http://www.techpowerup.com/forums/showthread.php?t=112556. It worked for me on me on windows 8, right now I'm able to actually open more than 4 tabs at a time with RDM using around 1242MB of RAM with 11 tabs opened.