I as a rule don't like to disparage things but what you hear is the truth. Boost 11 is unworthy of Platinum. CL will run it into the ground. 

Concrete Limiter sounds WAAAAAAAAAAY better than Boost 11! ...... I mean WAY!!!!!!!

I have a question ..... If I replace the Boost 11 with the CL in the master bus will I need to run the Brickwall limiter in the fast mastering mode also or is it not necessary.

I don't know what Fast Mastering Mode is. I do know that the CL is a brickwall limiter.

if you have it, maybe try the Nomad Factory 'BT Limiter' (it came with Sonar X2 or X3 I think).
It has all the basic controls (Boost 11 and Concrete Limiter are missing quite a few).
Personally I don't like Concrete Limiter (don't shoot me CL fans !) but admit at first it sounds great, but hearing it back later I always notice some lost on transients/drive/dynamics.
I like to control attack and release (not that I can yet ), to me they are the throttle and brakes of any compressor/limiter.
Just mentioning you don't HAVE to use a Limiter, I get better (ok, less worse) results sinds I stopped Limiters and just let it clip, plus it's easier.
Anyway, good luck
 

Boost 11 may be my least favorite compressor ever released by Cakewalk. It's not that bad if you use it gently, but the GUI makes it looks like you can do more than what will actually sound good. By the time the GUI reflects it visually, the sound is already messed up. I know we are supposed to mix with ears, but it is natural to expect the visual aspect to have some use.