The benchmarks look good. This article (https://www.phoronix.com/scan.php?page=article&item=ubuntu-2104-clear&num=1) says:
Out of nearly 100 tests, Ubuntu 21.04 was about 4% faster than Ubuntu 20.10 overall while Intel’s Clear Linux had a 8% advantage over the new Ubuntu 21.04 “Hirsute Hippo” release.
Have you tried disabling the Spectre/Meltdown mitigations?