I beleive splitting 10's is less risky than doubling A9. Double A9 and draw a low card and you could easily turn a winning hand into a double loss hand if the dealer doesn't break, and since the index is high for this play, you most likely have out max bet. For this example we will say 10 units. So you turn 10 unit win into 20 unit loss. (a 30 unit swing) If you split 10's, it is possible to do the same thing, but it is also possible and very likely that you will draw a high card to at least one 10, so there is the possibilty of win one, lose one. Net result, turn a 10 unit win into a push. (a 10 unit swing)