Exhaust on a GSXR1000 K6

[not_a_beast]

I'm looking for a new sound and don't feel like spending the money on a full system. So I got to looking at a Yoshi slip-on but I see that if i go that way, I'm going to lose that little valve right before the end can. Is that going to cut down on my midrange power? I've heard that valve helps with back-pressure in the mid revs and keeps the power linear. Is that gonna change with a slip-on?