Comment 1 for bug 325591

Yes, software rendering would cause a major performance regression.

Unfortunately, it's impossible to begin guessing why it would do that without seeing logs and other info about your hardware and software configuration.

Since this bug is pretty old and lacks the info needed, I'm going to close it. If it is still an issue, make sure to use the command 'ubuntu-bug xorg' to report it, which will attach the necessary logs to debug it.