The early Atoms weren't P3 based, they were an original low-power design and actually quite a bit slower than the P3 at similar clockspeeds. Though a lot of the unpleasantness of using those machines was more from the extremely anemic GPU which has also improved considerably since then.

Here's a benchmark comparison between the Atom used in the EeePC 901 (N270 @ 1.6Ghz), the GPD Pocket (x7-Z8750 @ 1.6Ghz), and a 1.1Ghz P3: https://www.cpubenchmark.net/compare.php?cmp[]=2968&cmp[]=13...

The P3 is slightly faster than the old Atom in spite of the lower clock, and the new one is over 2x as fast single threaded and over 7x as fast multithreaded.