B&W 603 vs Martin Logan 40i ?

Yes.  I worked for Magnolia and heard both, and my recommendation is neither.  The LSA-20 Signatures are available here on sale for $2299/pr and they’re at another level entirely from these.  Not even in the same ballpark.  Best of luck. 

I was hoping to get a pair that has a center channel of the same line. I don't see any center channel sold by LSA unless I am missing it.

I think your idea of the Evo 4.3 with the Evo 4.C center would be very worth exploring, and through places like Crutchfield, Music Direct, etc. you can try them at home and return them if they don’t wow you (but they probably will). Another great option would be the SVS Ultra speakers that offer a very generous and truly risk-free trial period, and as they sell direct you’re getting a lot of quality per $ spent. Last, and also sold direct, the Ascend Acoustics Towers with their Sierra Horizon Center would be a killer front three. Personally I’d take any of these over the other two you’re considering. The Paradigms would be great too, but they’re quite a bit more expensive and not sure they offer enough of a performance improvement over these three options to justify the added expense. Hope this helps, and best of luck in making a decision.