I have a K5 and it's light. Much much lighter than my corvette 4 strings (these are boat anchors), about the same as the ACG (surprisingly light for a fancy 5 strings single cut). Probably the same weight as the SR505. I don't think you could get a lighter 5 strings. The body is small and comfy, the string spacing is pretty tight (16.5, 17 mm?)!
I'd go with the ibby if you like it, they are very very well designed (weight, balance, feel, neck, hardware, even the pre is decent), and well priced. If it feels right for you, and you can get it at a good price, go for it. One slight issue with the K5, I don't like the Elixirs they put on (coated strings).
If I can grab some scales, I can weight the K5, but it's definitely on the light side.
for fun