Jobo 2553 - How much fluid?

I've been trying to figure this out and even searched before posting. My Jobo 2553 holds two reels with 4x5. The volume for rotation is printed on the drum "640/1250". I've found various opinions on how much to use that vary from 450ml to 800ml. I've also noticed a few warnings about overloading the motor by using a liter or more. Has anyone found a good volume that works well with this drum? I'm planning on processing 12 sheets of 4x5 in D76 or maybe Rodinal.

My 2553 says to use 560ml for 8 sheets on 2509 reels. I don't normally develop 12 sheets at once mainly because I don't shoot that much. I load the inner and outer tracks leaving the center empty and use roughly 600ml. D-76 is cheap enough to use more than necessary to ensure complete coverage. 600ml is not enough to overload the motor but I do help the lift when I empty the tank. With 12 sheets, 640ml should have enough activity to do the job but why not try more, like 800ml, maybe?

when using d-76 stock you need at least 75ML of stock solution per plate. that makes 900ML the absolute minimum.
the capacities on the Jobo labels are designed for color processing where you do not need more chemicals if you have more film, because the exhaust alot slower.
the earliest version of Jobo motors can take up to 1.25L, and the newer ones can handle alot more.
in any case when i do 12 plates i use about 1 Liter of d-76 stock.
if you are using d-76 1+1 you need to make sure you still have at least 75ml stock solution per plate, which will bring the total to 1.8L, which is more then the recommended max capacity, and not that usful anyways, the point being that if you dilute that you cant do 12 at a time.
hope that makes sense.

May I chime in with a question along these lines too ?
I have a 2523 tank, which take 270mL to do 6x 4x5, and will do 2x 35mm also in 270mL.

The 2553 needs 560mL to do 12x 4x5, but 640mL to do 4x 35mm ...

How does that work ?
Once the tanks are horizontal, the height of the fluid SHOULD be the same to cover the film ...

when loading 4X5 in 2509 reel, the highest point of the film at any given position when horizontal is X height.
when loading 2502 reels with a 36 frame long 35mm roll of film (or 2X 120 films or 1X220) the highest point of the film in the reel when horizontal is about 5mm higher.
the higher the film is inside the tank the more chems are needed to make sure it is fully submerged.
if you have the 2509 and 2502 simply put them side to side and note how much closer to the core the 2502 spiral goes, as appose the the relatively distant inner track of the 2509 from the core.

in the olden days when some poeple used to use 2501 reels, where one can load 2X35mm rolls per reel, the film is almost wrapped around the core and when used in 2553 tanks it needed even more chemicals then 640ml to drench the films.

... but in the 2523 it takes the same volume for 6 4x5s and 2 x 35mm (which I've used in those configurations and with great results in a CPE2)

thats true. i think the question was about 2553 in the OP.
the bottom of the 2523 tank is not flat, it has an indentation. this takes up the space that makes the discrepancy in the 2553, which has a flat bottom.