When we looked into testing for our DD at 3.4, the private tester we consulted with told us she would recommend testing at that age only if it would change our educational decisions for her. We went ahead with it because her preschool teacher was recommending acceleration, and we wanted to make the most informed decision possible.
With her older sister, we're going to do testing at 6.10. We weren't planning on it, because she seems perfectly appropriate, happy and sufficiently challenged at the traditional grade level. But we decided that she deserved us having as much information about her as we had about her sister, so we're going to go ahead with it, even though we don't anticipating it changing anything.
I guess that's all to say that if you feel like she's in the right place for now, I might hold off a bit if it were me, but definitely pursue it later, or now if you suspect she might need something different.
