I can't see much point in getting a CL and 40mm given what you already have. I doubt there's too much of a difference weight-wise in actual practice between the CL and an M. Given that, why would you choose to go out shooting with the CL in preference to an M3? If it's purely for the 40mm then I've heard that you can use that lens quite successfully on the M3 by using the 35mm framelines. As you're probably aware, the Leica frame lines are quite conservative, showing a good bit less than you're actually going to see on film. This means that the 35mm framelines are a reasonably accurate guide to what you could expect to get shooting with the 40mm.
I appreciate that this isn't what you're asking but might I suggest picking up a Hexar AF? It's well made, has a really superb 35mm lens, a very good viewfinder (probably not as as good as an M's but good enough) and will set you back less than the cost of a CL body alone. I have one and, despite not being a rangefinder-type of guy, I can't bring myself to sell it because the lens is so good. You can see a few black and white landscape pics I've taken with it here.
The Hexar, unlike the CL, gives you something you don't already have - an auto exposure, AF rangefinder-type camera. You might not want to shoot like that all the time but sometimes it's nice to have a change!