In particular,
RF 70-200mm f/4L (to debut any day) vs. RF 70-200mm f/2.8L
RF 24-105mm f/4L vs. RF 24-70mm f/2.8L
If cost AND weight are not a factor, it's no brainer except for a bit of reach issue with the latter. However, cost AND weight are significantly different. Cost, I can manage better, but weight is more important as my aging (and aching) body requires lighter carry load. Here are the cost and weight differences:
RF 70-200mm f/4L = 1.5 lbs and $1,599
RF 70-200mm f/2.8L = 2.35 lbs and $2,699
RF 24-105mm f/4L = 1.54 lbs and $1,099
RF 24-70mm f/2.8L = 2.7 lbs and $2,299
On my R5, the first group gives me up to 7.5 stops of image stabilization. For the latter group, up to 8 stops of image stabilization. What this means is that IS pretty much eliminates low light shooting concerns and that leaves the advantage of f/2.8 to better bokeh.
Of course, in spite of 7.5 or 8 stops of IS that the R5/lens combo gives, f/2.8 definitely has the advantage both in low light shooting and bokeh. The question is whether what advantages there are, are worth the significant cost and weight differences. Such question was simpler to answer in the EF days. You need to shoot indoors and in low light venues, you cough up the money, hardly a need to question. With the RF future, however..... What are your take? Given the IS stops you can get using these lenses with the R5 (or R6), would you still cough up the extra $1K+ for the f/2.8 version? One thing for sure, the R5 (R6) and RF f/4 lenses are as perfect as one can have for travel photography.
