iF you like a 5dx ONLY for filming... belive..forgeti!...
there are many anothers way more and more usefull and good for LONG filming...with 4.2.2 10 but 4k 60p or more... example a GH5 (1200 euro).. (or gh5s)...gh5 have a super stabilizator on body... with 5d3/4 you can forget .. (lens with stab. are good only on photo mode!)
if you like RAW blackmagic , zcam and anothers...have nice FILM camera..about 1500-2000 euro...
why I say that? because that are really moves camera , no limits like the 5d3/4...
the canon' are super IF YOU do photos, and you do somenthing also for filming...but buy ONLY for filming for me is crazy!
ML on 5d3 is super...but expansive,with lot troubles and limits... CF 128Gb "good" for raw14 bit are expansive, cna recordinf circa 20 minutes and are full..
and at home before converting the ML.RAW in your edit program....you can take holiday, ML sometime stop recordingk or ate home you have bad surprece with bad frames ecc...if you read in this forum you found TONS of this troubles, and is a TRUE.... so...ML is good if you film somenthig you can do 100 times again, with lot time, and free of stress... BUT if you like do sometihnig for work, (wedding, concerts, and lot of events where you can't do errors...) YOU CAN'T USE or if you do is a BIG risiko. THAT'S shit.!!! because 5d3 whithout ML have a bad FHD...is like a 720p strech to 1920p 8 bit... a IPHONE do better today!!!....BUT in raw, 1920 is really 1920 and pretty images... SO, dream is to use on work ...RAW ML also for weddings, and all the things... but dream, and you know why...
SO...a blackmagic camera, or gh5 ...in this way are 1000 times better of 5d3 or 5d4 (with codec canon...) NINJA ?!? I can understand ONLY if you need HOURS of recording...but not for have more quality...the output HDMI 5d3/4...have no 10 bit /4.2.2. PRORES recording always of a 8 bit output..so the quality IS THESAME of what recording the camera on CF/SD...!!
wht's better 5d3 or 5d4 ? well..the 4k of the 5d4 is better of the 1920 5d3... BUT the best of the 5d4 I think are in photos way...
I dont' know how much you pay a 5d3 or 5d4 used...but look well also the another cameras, because if you like film with good quality and no some big limits of canon 5d....is the only way.
I have the 5d3 buy 1st for do photos, but IF was needit only for filming, never was buyng!!!
this my opinion!