You can't really compare a downstream fork (and especially not a rebasing one) to its upstream though, that's not apples to apples, because the fork can (and often does, also outside of this particular instance) include all or much of the upstream work too. Besides, Core is still the reference client, so you can't really compare any other Bitcoin client to that.

What you can do is compare btcd to libbitcoin, or compare knots to Peter's libre-relay if you want apples-to-apples.