Assuming you are on v9, you may want to keep your block size at 128 KB. I just received an updated best practices guide for dedupe from CommVault and it states that 128 KB is the "new recommended" block size for dedupe:
"Dedupe Block Size: 128K; New Recommendation based on increased capacity of DDB Engine and last block fix"
I confirmed with our local CV SE that 128 KB should be used for all types of backups (file system, e-mail, VMware, databases). This seems surprising to me but unless I hear otherwise I will take this into consideration going forward.