For what it's worth, Mouse is much more than 25% faster than Moose (at least it is on machines where it's been compiled with XS; Mouse::PurePerl is very slightly slower than Moose). While it appears to offer good compatibility with Moose; this is on the surface only. Things start to break if you try to consume a Mouse role in Moose, or extend a Moose class with Mouse.
Moo has far less of a start-up penalty than Moose, but when it comes to running speed, isn't quite as fast. On the surface it appears less Moose-compatible (but see MooX::late) but it's designed to be able to interact nicely with Moose. You can extend Moo classes with Moose, consume Moose roles in Moo, etc.
The only places I can see big scope for Moose optimization are:
I've published a couple of modules on CPAN that might be of use if you're trying to eke a little more speed out of a lumbering Moose...
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