I shoot a D3, a D300, an M8, and the G1 and G1F; the latter two are now my favorites, although I don't do the same kind of shooting that you do.
I don't think anything short of the M9 will make you happy if you want DR in the range of the D3x, with a good pixel count (18mp) in a lightweight camera. However, in my experience, very few people who are happy with their DSLR will also be happy with an M9 -- although it doesn't work the same way the other way around; that is, most people who consider themselves to be primarily M8/M9 shooters usually also have a DSLR, for the flexibility which is so lacking the the rangefinders.
There are focusing problems inherent with rangefinders which you may find troubling (for example, the bodies must be calibrated to the lenses, and sometimes, it's hard to get all the lenses working at the same time.) There are also framing problems, since rangefinders are inherently less accurate in framing than are DSLRs. Leica has a large number of fanboys (of which I am often one), but if you read most neutral reviewers, you'll find that most would suggest that the Leicas are not among the best for ISO range. The longest M lens is a 135, and most people don't use it because it's extremely hard to focus at anything less than infinity. 90mm is more like the practical limit -- some would say 75mm. And, of course, there is no autofocus or live view. The longer of the two tri-elmars would fit your focal-length needs on an M8 (1.3x), but not on an M9 (FF). One other thing - the Leicas are not extremely light. Prime for prime, the lenses are heavier than the Nikons, though the bodies are somewhat lighter, though again, not exactly light. The Panasonics (and the Olympus) are simply not at the same level as either the Nikons or the Leicas, so if you're hoping for something that would resemble a D3x shot from them, you won't get it from them, though they are excellent cameras for what they are. And they *are* light.
One possibility -- most people think that Nikon will soon come out with a D700x (or something similar -- a smaller, lighter, cheaper cameras with the D3x chip inside), so you could wait for that. The other possibility is simply to buck up and carry the D3x, and dump some other equipment.
JC