no 1hp is not alot, if you have 90hp thats only a 1.1% increase in power, anyone who can say they can feel 1 hp is a lying, it might give you a placebo effect but its all in your mind

i would never ever buy an akra slip on, or any high end pipe unless its a full system, and i wouldn't buy a full system for a 600 unless i was racing it and absolutely had to have that extra couple horses, there isn't much to be gained on most modern bikes period through an exhaust because they are just so good from the factory but the gains are especially low on 600's, on the street you will just lose a little low end and probably not even notice the extra 4 hp you picked up at like 13k rpm... a 200$ slip on will give you all the sound and look of a $700+ full system and thats all you need on the street