updgrading from crop to FF - noise performance

Hi folks...

Apologies for double post - i accidentally put this i "open talk" by mistake

with the advent of mirrorless causing a plummet in the prices of new DSLRS i'm considering an upgrade from my 7dmk2.

About the only reason i'm half serious is that the mighty mk2 has pretty ordinary noise at high iso.

If i shoot in low light i use my 17-55 f2.8 .....(which will only work on a crop sensor camera)

So my question is this:

speaking purely on noise performance, and not about the other pros/cons comparing the two cameras...

If i upgrade to something like the 5dmk4, which has approx 1 stop better noise performance....and to get an equivalent zoom range for not outrageous cash....

i get a 24-105 f4L....

Am i defeating the purpose of getting the better sensor by having to boost the ISO by the one stop i lose in the lens?

have i got my thinking straight, or am i nuts?

Open to comments and suggestions...

Pretty much so.  There might be specific things between the two cameras but if you gain a stop going up and then go from a wide open at f2.8 to wide open at f4, you do lose it again.

From a different view, which is more important, the super high iso low noise characteristics of the latest FF cameras, or the amount of this super high iso performance you actually need and will use in your photography?  I can't really comprehend just what uses these super high iso ratings are required for. My uses of cameras just does not require them. I have used 3200 iso in some rare instances, so for me the additional super high iso with less noise would not be worth the costs and weight involved. But if your work requires use of really high iso and low noise and especially if long telephoto work is not a big factor, by all means you probably should consider FF or MF formats. It's not what the camera can do, it's more what you need it to do for your situations.

It's highly individual. For those situations I prefer to use flash or even my cell phone, but we each just to realize what we personally prefer, not what someone else tells us we should use.

My cell phone utilizes AI with multiple images and with f1.5 lens seldom needs over iso 400. I just don't try to photograph black cats in a coal bin.

A kinda funny story on that.  Last year at Christmas I was taking some photos of my Son and his family (him, wife, and 4 kids).  I took photos with a Nikon dslr apsc, my wife took some with her Canon SX730, and I took some with my iphone 13 pro. The area in our home where the photos were taken is quite dark, and the phone exif shows 1/40 sec, at 1.5, iso 500, no flash.  The dslr photos were with flash bounced off white ceiling and f5.6, 1/60 sec I believe.  Anyway, when it was all said and done, they picked the iphone 13pro photos for their wall print and for their Christmas cards that they send. But the biggest reason was that in every one of the iphone shots all six of them had attractive smiles and everybody's eyes were open which was not the case in the camera photos.  I read somewhere later that someone stated that they AI engine in the processing detected smiles and closed eyes over multiple photos and takes it on itself to utilize what it deems best for individual people.  You can make of that what you want, but it was amazing in this instance that out of probably 5-10 photos out of each camera and the phone, every phone photo was this way and none of the camera photos were this way with all smiles and no closed eyes.  Maybe they are just more comfortable when in front of a phone vs a big camera is another possibility. Anyway hope you enjoyed the story, if not, sorry to bore you.

Thanks everyone for your input...

I would have to say that the only time the mighty mark 2 makes me 'unhappy' is in low-light situations with movement....like night or even twilight sports...

This is really the only time i have not been able to work around the 'limitations' using some of your suggested methods

the conclusion i reach, is that to get something noticeably better, i'm going to have to invest in a new lens as well.

Thanks again for your input -it has been most helpful.