It looks like the J5005 is 30-35% faster than the J4205 on average. I haven't done any extensive comparisons of operating frequency, but I'm guessing the J5005 runs at roughly 5% higher frequency. So average IPC improvement over Apollo Lake is probably in the 25-30% interval. Pretty impressive. Using Geekbench 4 for comparison, the J5005 seems remarkably close to the IPC of the Nehalem-based Core i5-760.
This is indeed really impressive. Nobody expected this when Intel called it Goldmont+ which sounds like some Tick improvement in the range of 0-5%. If the Atom team is able to deliver another boost like this for the next Atom this can be a real alternative for cheaper Core based notebooks.