Generally it will add roughly 100 fps to the top velocity potential compared to the 223 shooting the same weight bullets, say 55 gr compared to 55 gr.
Barrel life also increases significantly but that is not a huge concern in the 223 anyway.
There should relly not be any need for receiver modifications, new barrel, I would recommend getting it fitted by a quality accuracy minded smith using a top quality live piloted match reamer.
Depending on what you want for this rifle, you may want to get the receiver accurized as well. If you want extreme performance, you would be wiser to start with a custom receiver from the start if you plan on doing a complete rebuild on a factory receiver. In the end, its money very well spent to go with a custom receiver based rifle.
Just depends on what you want out of this rifle, economical shooter or extreme precision. The 6-45 will do either very well.