I've just taken a quick test with 4.1.1 RC2. Performance seems a better ... But our layout is broken! It seems the heights of each "row" within a form has changed. So basically every form we're using is broken that way. The elements do no fit into the fieldsets anymore. With 4.0.7 it works!
Info: We're using the absolute form layout with the gray theme which is compiled as scoped version.