I have omitted knoppix64 and nostartsound cheatcodes. But the "nozram" is necessary. (Maybe because of my hardware?)
My test results: (20 boots in both cases)
1)
Code:
menuentry "KNOPPIX_V7.6.1DVD-2016-01-16-EN 64b hu London" {
    set ISO=boot-isos/KNOPPIX_V7.6.1DVD-2016-01-16-EN.iso
    loopback loop /$ISO
    linux (loop)/boot/isolinux/linux64 bootfrom=/dev/sda1/$ISO noswap  noeject noprompt lang=hu tz=Europe/London --
    initrd (loop)/boot/isolinux/minirt.gz
}
Code:
knoppix@Microknoppix:~$ free -h
              total        used        free      shared  buff/cache   available
Mem:           3,7G        102M        3,0G         76M        568M        3,4G
Swap:          2,7G          0B        2,7G
knoppix@Microknoppix:~$
/home total: 2,9 GiB
/tmp total: 2,0 GiB
I use "noswap" because I do not have any swap partition or file (I do not want to use my HDD as memory).
In this case Knoppix crashed 6 times. Crashed: the system crashed at the point "System Setup... OK" (boot screen). So that I could switch off the PC only by force (holding the power button down for seconds).
2)
Code:
menuentry "KNOPPIX_V7.6.1DVD-2016-01-16-EN 64b hu London" {
    set ISO=boot-isos/KNOPPIX_V7.6.1DVD-2016-01-16-EN.iso
    loopback loop /$ISO
    linux (loop)/boot/isolinux/linux64 bootfrom=/dev/sda1/$ISO nozram noswap  noeject noprompt lang=hu tz=Europe/London --
    initrd (loop)/boot/isolinux/minirt.gz
}
Code:
knoppix@Microknoppix:~$ free -h
              total        used        free      shared  buff/cache   available
Mem:           3,7G         96M        3,0G         94M        605M        3,4G
Swap:            0B          0B          0B
knoppix@Microknoppix:~$
/home total: 2,9 GiB
/tmp total: 2,0 GiB
In this case Knoppix crashed 0 times.
I did tests with 32bit, too. But in this case there was no difference if I added "nozram" or not. (So I did not added.) With 32bit Knoppix crashes in other way but much more less. As I have said before, after the boot screen does not start X but only a black monitor.

About the persistence (Category:Hard drive Installation) I have a question. How is executed the saving process into the knoppix-data.img file:
1) continuously (I mean changes are written to HDD as we do it);
2) or changes are written in memory and only at shutdown are saved to HDD (into the knoppix-data.img file).
Although already I do not use any persistence, solving my "persistence" with scripts (to not carry forward the problems to the next boot), I am curious.
Regarding to my way of persistence, I would have a request to Mr Klaus Knopper. If we boot Knoppix from ISO file, we found on the desktop "mnt-system" folder (as when using a DVD disc). But in this case it will be more useful an "mnt-iso" folder. For example, I store my persistence script (executed manually after boot) in the same partition with the Knoppix ISO file, and reaching it would be more faster.