I have a modified Ninja .28(the GRP made one) and a 21 ninja. Both are great engines, but the .21 is more than enough for the 8ight-t.
But the .28 does offer a little more bottom end snap, but very smoothly. If you have a smooth throttle finger it is very easy to control it, even though it's a .28. Very high revving engine as well. I get 10-12 minutes out of both engines, using a GRP 3009 pipe and Team Orion V6 clutch. Short header on the .28 and a long header on the .21.