This problem has been studied and comes under wider block-cipher encryptions, examples are Mercy block cipher , Bear and Lion , and Simpira. My answer ties with Simpira block cipher case. Simpira has been recently developed to work on 64 bit processors (v2 is also available) which uses 128 bit x b , where b is a positive integer. Simpira is a cryptographic permutation that combines AES and Feistel structure. In Simpira cipher , the number of rounds required to achieve full diffusion increases along the b value , (12,15,21 rounds for b=1,2,3).**This means , to achieve full diffusion of wider size more rounds are required therefore performance will downgrade.** for further information: [Simpira][1] [1]: https://mouha.be/simpira/#applications