I think the T6'S are for a stock machine so I think either would be an improvment.
The T5'S are a awsome sounding pipe, I bought a set for my bike but the pro circiuts I have out performed the T5'S so gave them to my cousin.
The shear's are a great pipe I've heard, I'm going too buy a set when I get enough money and try them, I heard they add another 5hp.
So I 'll tell you this it don't matter about the type of pipe it's all about your mods.... :thumbsup: