Open Exhaust or full exhaust?

my mustang is not my daily driver so there is no concern of creature comforts...having said that i have had the car running on long tube headers with glasspack mufflers for a while (about 7 months) and the sound is great and i love it....but since i really dont see mustangs at all with exhaust like this i was wondering if there is something wrong about it...this are the style (not same ones though but more or less) that i am using...

i have equipment enough to run it like this, a list of mods of my car is:

Holley in-line fuel pump
holley fuel pressure regulator
Edelbrock 600 CFM manual choke carb
Edelbrock Performer RPM intake (port and polished)
Crane Cams camshaft, retainers, springs, 1.7 roller rockers
Ford Racing pushrods
Ported and polished OE heads
MSD blaster coil
MSD 6A
Ford Racing 9mm wires

maybe i'm missing a couple of things but thats what stands out...im just wondering if it would be better off with a complete exhaust or if it is better this way...sound is of no concern as people just dont mind a noisy mustang

no tickets so far.....i just want to know if im losing a lot of power because of this...because if i am then ill put some aftermarket exhaust and thats that...

its just that since ive seen the ac cobras running like that....i wondered why couldnt i do it since many replicas run the same engine i got