I still remember working with G5 towers in graphic school, they were quite capable for their times despite being a jet engine... then later on a 2011 MBP 13" was a long time carry machine for when I was working abroad (music related, sometimes photography in recording studio / concerts). And then I also purchased a base M3 Max 16" on day 1.
It is very difficult to quantify since these machines are so far apart in terms of tech. With the G5 when new, Apple was undergoing a transition from Classic OS to OS X UI, without access to Intel hardware yet, at that point in time a G5 tower was seriously a better productivity choice against something like a Windows 98 PC especially for Adobe workflow. I don't even think Lightroom was annouced by Adobe yet, Apple hasn't released Aperture, so photo editing was all about Photoshop, and the PPC Macs + OS were tuned for it.
But with the transition to Intel things changed very quickly. The unibody gen of MBP particularly were so good, the chips are already Intel Core i5/i7 instead of the initial Core (2) Duos, the advent of Thunderbolt, and Mac OS Snow Leopard etc... this essentially moved the photography workflow that was previously only possible on workstation Macs to a laptop. And then there is the famous 17" which was simply exotic at its time (though mine was a 13", as my role was being portable as much as possible).
After that I have been building my own studio / business deploying various Macs for both myself and employees, the dark age of touch bar MBPs and the stagnate of desktop Macs... fast forward to Apple Silicon, the 2021 14" 16" M1 Pro / Max was such a homerun in design that they really didn't need to touch it for a few years, and only put in more power inside which is where we got the M3 Max. This 16" I am typing on is as close to a perfect laptop experience as I have ever had. But you have heard all that anyway. Doing edits in Lightroom Classic never felt so spontaneous as on this laptop, and I have a M1 Max Mac Studio also, I can tell a slight edge in responsiveness on the M3 Max. But seriously all Apple Silicon Macs are ridiculously fast for photography anyway, even a base M1 Air. The Intel Macs right before them felt like a joke in comparison (yes I have first hand experience with the latest 2019 MBP 16" i9)
So to answer your question. If I were to put them in numbers:
Power Mac G5 - say this is a baseline 100%
MBP 2011 - easily 150-200%, but it is a laptop so it was quite a feat at its time
M3 Max 16" - 1000% if not more. In fact it is close to infinite, there is virtually no wait time for LR workflow when culling and doing adjustments.
When you get your 16" you will understand. It is just a joy to work with. Medium format RAWs feel like nothing, and I mainly shoot Nikon D850 (14bit 46MP RAW), it is so smooth I sometimes thought it didn't register my click. The only time I get to wait is during import (preview generation), stitching panoramas and HDR bracket merge, and the very new AI Denoise. But these are supposed to be data crunching or cutting edge tasks so it is fine. I still remember having to manually merge panoramas in Photoshop 7 or something. What took 3+ hours of intensely focused manual labour is now like 30 seconds of coffee sipping.
