I haven't had these conditions firsthand, but here goes...
Clogged cat SHOULD(?) restrict more at higher RPM & higher load. That's when the exhaust flow rate is highest.
People usually describe EGR problems as stumbling - not smooth.
'05 Saab 9²x aero (RIP)
'09 Saab 9³ss
'10 Saab 9³sc
my kids have Civics