I think you can use the Arrow headers with other cans. It should work because you can buy the Arrow header and can separately, which means either should bolt up to the stocker and other after market cans.Those graph are interesting in that they all show a loss of torque in the low end. I think thats just for the slip on, and a header would address that.
Unfortunately, LV doesn't yet make the full system for the GP... unless you can mate the GP pipe to the EVO header? Dunno.
I think you can use the Arrow headers with other cans. It should work because you can buy the Arrow header and can separately, which means either should bolt up to the stocker and other after market cans.
I've seen one or two dynos for slip Versys cans, the graphs look a lot different than the Ninja. It seems like exhaust mods have a much more dramatic increase for the Versys compared to the Ninja. There's a before/after dyno chart somebody posted here that shows a 10% gain in torque, top torque is reached much earlier and stays up there. So you gain 10% more torque and you get it several thousand rpms sooner than the stock can.
I like the first video clip much more than the second. You're right, it's not too loud at all, but it's definitely louder than stock (in a good way). The second clip sounds sort of strange, when he lets off the gas.