Hi,
I am not sure I can get my hands on a list that diffs between the two card's features (beside BW) but for fact i know that there are quite a few including off-load engines and other scalability-related features.
checkout the product's pages:
ConnectX2: Mellanox Products: ConnectX®-2 VPI with CORE-Direct Technology
ConnectX3: Mellanox Products: ConnectX®-3 Single/Dual-Port Adapter with VPI
i am sure that after reviewing you would agree that there are new features. All couldn't be enabled without the HW support.
Thanks!