If you go the tube or macro lens route, just remember that the depth of field will be VERY small. Macro photography is a challenge, and even the best at the craft will get out of focus shots, so take lots of shots and pick the best! :)
I use the 300 PF with TC for insects, it gives me very close focusing distance. It's very sharp, but not as sharp as the 500 PF. It also focuses a bit slower.