There would be a difference to the yeast, but I am not sure it makes enough of a difference to worry about. I wouldn't go above 1.040 though, I think it is just a waste of DME. I make my starters with ~10% DME and 100% water, which should have SG around 1.037. I should probably cut back to 8% DME. wait that's 110% Tom, how do you manage that?
I make the starter with some amount of water (100%) and use 10% of the weight of the water for my DME weight. I wrote it that way because the gravity is different if the DME is 10% of the water weight vs. 10% DME and 90% water. Confusing I guess, but that's the way I do it.