Borla will have rumble, but it will also drone. Guaranteed. Anyone who tells you otherwise it is just not true.
Top 3 CB systems by popularity for the C7 are Corsa, AWE and Borla in my opinion, and that is not in order by any means.
If you have the money, Akra makes a real nice setup.
AWE is the classic sound and price is not bad, Corsa is more exotic and costs more $$