Size of encrypted AES CEK in CMS block
(moved from comment, expanded slightly) 

(AES) Key Wrap is not the same as normal data encryption like CBC or GCM; it does quite a bit of remixing, and adds exactly 64 bits to any AES "plain key" (here 256 + 64 = 320 = 40 bytes) even though it uses the AES algorithm which has a 128-bit data block. See http://tools.ietf.org/html/rfc3394 and the relevant example in section 4.6. 

The KEK is indeed 256 bits in this case, determined by the algorithm id-aes256-wrap, but that key doesn't appear in the message; it is derived from ECDH key agreement, using the originatorkey in the message (in the BITSTRING at offset 54) and the key in the recipient cert identified in the message.

The ECDH key(s) here appear to be on a 521-bit curve, presumably secp521p1, although on looking closer I notice it is not encoded in the AlgorithmIdentifier for originatorkey as is normally the case for encoded public keys. If the ECDH curve were substantially smaller, then the key-agreement strength would be less than 256, which would make the use of a 256-bit CEK in a sense wasted.