It seems that many Topre aficionados advocate 55g switches. In view of this, it is surprising that 55g Topres aren't more prevalent. In fact, the opposite is true. The 45g versions are found on the RF 87u EK edition, on many of the keys on the RF variables, and on the HHKB Pro 2, microTron, Leopold FC660C, Type Heaven, and Novatouch.
I feel like I ought to prefer 55g switches in order to be alpha, macho, and cool, and I do prefer them at times, but sometimes it seems I can type better when using 45g Topres. As some others have suggested, 55g switches might be fine for the short term, but for long typing sessions and/or when one is otherwise fatigued, 45g switches could be better.
The most direct comparison I can make is between the 45g and 55g versions of the RF 87ub with the same keycaps on each board. Under these conditions, presumably the only difference between the two boards with respect to typing sound and feel is the switch weight, and the difference seems fairly subtle. But here again, it is difficult to make long-term predictions based on short-term assessments.
In my case, I like to rotate among my favorite keyboards anyway. I think I might start with a RF 87ub 55g in the single workstation in my home office, put the other RF 87ub 55 in one of my two workstations at work, and place the RF 87ub 45g "EK Edition" in the other workstation at work. At work, I need to move from one workstation to the other at various times during the day, and this will give me many opportunities for making continual comparisons without needing to plug/unplug keyboards.
Currently, the favorites in my rotation include the RF 87ub 55g, RF87ub 45g, HHKB Pro 2, and IBM Model F XT. Ah, the luxury of first-world problems! I do appreciate it!