Geekbench for the 3 is 326 single-core/559 multi-core vs the 4’s 803 single/1250 multi.
The 4 had a 1.4 GHz A6X vs the 3’s 1 GHx A5X. The 4 was the first big iPad with the Lightning connector.
My iPad 3 was always a slow pig of a thing.