hey raid,
i'd recommend either the 75 lux or 35/1,2. Both render uniquely and very beautifully; as a sonnar lover either will grab your fancy in terms of the images, though the 75 gets the edge in terms of DoF. Inasmuch as i love the 35/1,2 look, it was very large for a RF 35 -- yet alone for an all-round travel lens. Of course the 75 is a big bertha, but that comes with longer FLs, so it is not a big contrast in size/weight from a 90 etc..
As a 50 FL guy, I can say that you will find shooting the 75 to be a sweet spot.
But if you are determined for a lowlight all-round 35 for travelling, I'd recommend either the pre-asph lux 35 [over 2,3M in SN] or the CV 35/1,4. Both are much more compact. Both will do service in a wide range of light. The pre-asph lux has a very distinct glow and grittiness. Roland, jon and others can tell you loads about the cv 35/1,4.
If your budget is not more than 1500, then the lux 75 is not attainable. If this is the case, I'd go with what I consider to be the best all-round 35.
Hope this helps,
Thomas