Same here too. I noticed it the first day, simply opening a new project with RT enabled, where performance was worse. I thought it could be due to new RT features.
Right now, testing on a non-RT project. Being simply a Default map template, with some objects, and with some totally static lighting, project goes from 520fps to 430fps when in 4.26. That a huge 20% drop, in concordance with the 20-30% performance drop all other users are reporting.
Yes, we should profile to see where the drop is, but I have no time now, and, anyway, it’s evident something is happening, as it occurs in the most simple scene.
Regards!