32 megs is a big file now? I mean some might not have undo buffers that large but most will only start to choke when the operating system does.
Anyway I tried out a whole bunch of hex editors as part of my GBA and DS docs. Assembly wise you will be lucky to get more than basic X86, mac style powerPC and maybe 8080/Z80 unless you go in for a ROM hacking based hex editor in which case you might get SNES or ARM7TDMI and ARM9. Some also include Java support but I am not sure I want to call that disassembly at this point. MIPS wise you are probably looking at purchasing a copy of IDA (though I can not say I have seen what goes for MIPS on the free one lately) if you need that sort of thing.
Custom encodings to what level? I have yet to see a general hex editor (paid or otherwise) that supports ROM hacking grade custom encodings. Single byte to single UTF8 character sure (and you may not have a nice interface to add a lot in) but multibyte or multicharacter is a struggle and a proper decoding if it has something like an encoding change flag is right out. Though it is also a problem on ROM hacking editors if you have two characters decoding to the same letter and need to change it then give up now or learn the encodings to the point you can decode them in your head.
On the flip side though I love all the ROM hacking hex editors in their own way they are not about to be my general use hex editors by any stretch (sketchy undo, a general lack of functions and not always the most stable).
HxD ( http://mh-nexus.de/en/hxd/
) is my "I am sitting in a client's place and of course windows does not even have a basic hex editor built in" choice of hex editor.
It has a truly basic compare function (more advanced ones will attempt to determine where the file picks up again and can do it on sections at a time*) but as long as you are not comparing cross region, 1.0 to 1.1 versions or games with a filesystem and do not want a detailed analysis you should be good.
*copy and paste in a new file being the obvious solution to this issue.
Freeware wise of all the ones I tested it comes down to three options (plus a copy of HxD just because)
The old classic but it has a serious scripting engine that punches above even the likes of Hex Workshop and 010 editor (the two best paid editors useful for ROM hacking conventional consoles- xways winhex is great if you are recovering hard drives at NSA/GCHQ level but not so much for ROM hacking uses). Also has a basic encoding converter, once a file is open click search and then "character conversion". The scripting engine does seem to pull focus from the GUI so you may not have the best time if you just want to invert your current selection or something.
It looks horrible when you first boot it but take 30 seconds to configure it and it sits as my general use editor now (well when I do not have hex workshop it does). Sadly it does not even have a basic file compare or the ability to open two files at once so it might not be of much use to you.
(if you are having trouble hit me up and I will sort various mirrors out).
Despite being abandoned years ago it could still give many of the commercial ones (certainly other than the three mentioned thus far it beats all the ones I tested).
Has compare functions almost up there with hex workshop's, has some scripting and supports custom encoding (read the help but generally click "view -> character translation" and make it custom with "options -> plugin settings -> custom character translation table"
Combing the four I find just about equals the commercial editors save for XVI32's scripting which is really nice.