I don’t think your dynamic range can be improved with ISO. There are post processing tricks you can use (e.g. gamma), but otherwise the dynamic range is based on the quality of the sensor and the electronics responsible for converting the intensity of light on each pixel into an electrical signal. More on reddit.com

R3 has a slight edge (1/2 stop or less I think) due to the BSI sensor, vs the FSI sensor in the R5, R6, R6II, and R8, but I don't see a practical difference. More on reddit.com

So I am really curios to know if switching to the new R-Series is a game changer in such aspects or is it even with the new sensors quite the same play. The difference is significant, but not necessarily so apparent until you're making adjustments to RAW files—that's where you'll really see the improvements—and it's mainly at lower ISOs. Here's a chart showing the R5 compared to the 6D and 5D II you mentioned. At base ISO, the R5 has an extra 2-1/2 over the others.but beyond 1000 it's not significant. More on reddit.com

I'm using R6 for 3 years and R6ii for 1 year now. I'm using both for professional video use. Answering your questions: Canon Log video is HEVC 4:2:2 10-bit. This means no Nvidia or AMD graphics cards have hardware acceleration for this video codec (only latest Intel graphics and Apple M1 or newer). If you have a stronger CPU, you can edit without proxies. Otherwise, it's required to have proxies. I don't have to use proxies for simple projects. If you underexpose Clog-3, your shadows will be just grey areas of noise. Use the histogram and assess the ideal exposure. On most shots, I tend to overexpose by one or two stops if require more details in shadows. One thing I miss on the R6ii is the lack of Clog-1. If I can't plan what shots are going to be in slow motion I prefer to shoot everything in 50/60fps with 360° shutter and deliver great looking full speed footage and a bit blurrier slow-mo. I rarely use Focus peaking while manually focusing but it's alright, I guess. EF adapter is great. Lightning fast focus on EF 16-35L ii, 24-70L ii, 70-200L ii. I wouldn't say RF lenses are any faster, though the majority RF lenses I work with are non L fixed lenses which all have slow AF, and the bulky 28-70L F/2.0, which has fast autofocus. I love how the end result looks when an experienced colorist does the final grade. Overexposed footage is way cleaner, but pushing it too far does harm as well (clipping aside). You can also just apply the official Canon LUT, tweak the curves little, and it looks pretty good on its own. More on reddit.com