I wouldn't expect Moo to gain you much over Moose in terms of runtime performance, except in the very simple cases where Moo can use Class::XSAccessor instead of generating a perl accessor method. What you probably want instead is to profile and selectively remove type constraints - perhaps only for runtime but not for the test suite. Consider:
package MyApp::AssertIsa;
use strictures 1;
use base qw(Exporter);
our @EXPORT = qw(assert_isa);
sub assert_isa { $ENV{SOMETHING} ? @_ : () }
and then
use Moose;
use MyApp::AssertIsa;
has foo => (is => 'ro', assert_isa(isa => 'Bar'));
and flip the relevant env var for your test suite (or perhaps use one of the test harness env vars to trip it automatically for t/)
