This has been covered many times previously - please use the search function.
DJI 3510's v 3510H are 350kV v 420kV respectively.
They both give a maximum of 2,100g of thrust (assuming 6s swinging 13x4.5's). There was a very slight bump in KV rating on the V2 motors but this was more of a marketing gimmick rather than a real world power difference.