The looks of this, it looks like the link with slip on is pretty competitive to the full. Am I reading it wrong?
Its a really tough call if you just look at them overlayed like that; was meant as a quick comparison only. You really have to overlay them in photoshop. First you line up the stock HP runs, ignoring the torque curve; you can then see the differences where one outperforms the other in HP. You then have to do it again for TQ and line up the torque curve while ignoring the HP curve and compare them that way for torque. You can't just overlay them like I did in the animated GIF since the scaling is off between the two PDFs of their charts.
I'm not here to push you one way or the other, ultimately it is your money. But for me it was well worth it especially since I haven't had to mask the low end weakness by regearing my 5th gen (still 17/39). I can pretty much gas it in 6th gear cruising around town and have no bog or have to downshift to get into the power. All the claims Akra has made about their gains were there and then some and I backed it up in my own dyno testing as shown in the link posted earlier.
Again, look at data from several areas, not just mine or what I present. I had various slip ons on my 4th gen before putting a full on - no comparison whatsoever. Had I just put the full system on from the get go like I wanted I would've been way happier. On my 5th gen, I wasn't going to make the same mistake again so as soon as Mike @ Riders Discount was taking orders for the Akra Evo, I gave him my wallet and had one of the first few in the country. Don't regret it one bit either.
You can always buy the slip on and upgrade to the full later on. Or you can get the Graves slip on and then upgrade just the header later on too with their Link system or whatever they call it.