SR is promoted as the "next step" intro to CP helis. But it sounds like it's basically just tuned down in the radio. The 400 will be more stable because it's larger and can be tamed in the radio and with flybar weights, the tail will be more solid because it's belt driven, not motorized, and it will give you more room to grow.

CP helis are more difficult to fly and you can learn on the Pro2. You can replace the TX with a DX6 or 7 and program the controls to your liking, that makes a big difference. Also, if you haven't already put flybar weights on all the way out, that will help stabilize it.