Not much to write, electric locomotive moves super slow while having a power cart giving it power (atleast EU from CESU) no matter what speed i select in the locomotive GUI. Also the EU loader does not work on MFE cart (but it works on the others)

I think you need a transformer upgrade in the EU loader to charge an MFE cart, at least that worked in beta 3, have not tested in beta 4 just yet.

But yeah the balance seems a bit weird and MFE carts are so heavy that they are super buggy I feel like (could be another reason tho). Wanted to wait a little before making an issue but since you report similar things I might as well comment on here.
Had issues with the MFE cart not linking right to the train and glitching inside of the train being stuck once I got them to link and also couldn't use the crowbar to rotate the MFE cart on rails by hand.

MFE cart isn't rotation aware. Rotation is handled by vanilla code.

Possibly related to #1577

Duplicate of #1624. See #1577 also. The MFE cart is definitely getting a throughout check.