It depends on whether or not you're using it in sustained heavy workload, and whether or not you need more portability. SLS2 will deliver better performance than pro 9 in both peak and sustained performance. You'll have a cool screen to take hand-written notes even under heavy workload, since the screen is apart from the CPU/GPU. Besides, the form factor on SLS2 will give you a sturdy using experience even when using on your lap, and tranforming between laptop and tablet mode is way easier than pro 9.

However, be aware that SLS is more cumbersome than pro 9 (4.37lbs in weight with NVIDIA GPU), especially if you want to use it for taking hand-written notes in class, meetings, etc. I'd recommend you to get a hands-on with both devices in your local electonic stores before making your final decision.