regardless, of what you do, as soon as you put the aftermarket pipe on, you WILL lose low down power.... an example is, I went for a ride with one of the guys from the shop where i got my bike from....he was on the demo which had a slip on and nil other mods, ie no PC, no aftermarket filter, and mine is stock standard, and he could not stay with me until we were on the move. He himself was quite suprised at the level of difference when it came to standing starts.
Really, if you want it just for the bling factor, or want to use the bike on the track then go for it. But really, you will lose low down torque / power. Although the akra seems to be one of the best for limited loss in the lower end of the rev range, but.... it still loses power!
I personally love the sound / look of the aftermarkets..... but would rather not get the pipe until I had put enough away to do the mod properly.....which after doing a track day will be probably never! As all my spare $$$ will be on things I can put to good use on the track!
I know that I can't possibly use all the power that my bike generates now, let alone require more..... I am more keen on setting the handling side of things before going for power gains! ie. steering damper, getting the suspension set up properly..... all the things that will make my bike handle better with the power that it has, rather than getting more power....when I can't, and probably never will, outride the bike!