From what I have read, it seems that most people feel the Loomis BCR series rods are slightly more powerful than an MBR series rods of the same power. If this is the case, why are the BCR rods rated for lighter lure weights than MBR rods of the same power (BCR853 = 3/16 - 5/8oz and MBR843 = 1/4 - 3/4oz)?

I'll take a stab at this one but don't take my word at 100%.

The BCR line is their worm rod series and MBR is their "all purpose"series. Two totally different actions.

The BCR will have a faster tip then the same size rod in the MBR series.

I'll take a stab at this one but don't take my word at 100%.

The BCR line is their worm rod series and MBR is their "all purpose"series. Two totally different actions.

The BCR will have a faster tip then the same size rod in the MBR series.

I agree.  The BCR rods are considered "technique specific" rods focused on contact baits - jigs, worms, c-rigs, etc.  Loomis zeroed in on the ideal weight range for each particular model with these specific techniques in mind.  The MBR series, as stated, is more all purpose and has a more forgiving (moderate) blank than the BCR series.

I usually throw my plastics either weightless or t-rigged with a 1/8-1/4oz bullet weight. Would you guys recommend a 2 or 3 power BCR rod for this? Currently, I use an MBR 843 for these techniques (and everything else) and I like having the power to muscle fish in when needed.

I think the BCR 803 GLX is easily one of the finest T-Rig and 3/8oz. jig rods available.  I would definitely go that route over the 2 power rods - which are great and have their place, but in your case, I'd go with the 3 power.  If you prefer more length, the 853 is amazing as well.  

After buying a 6'6" rod for my first casting rod (making the switch from a 7' spinning rod), I realized that I definitly prefer 7' rods. I will definitly consider the 853. Thanks Bronzefly.