The GTX970m is a new card, so no one has three year's experience. Asus and Sager both make good robust products. I would expect the Sager to be significantly cheaper if the configuration is the same. The Asus is probably a little 'tougher'.
I was in a similar position to you and did the analysis and decided that the Sager NP8287-S was the best value solution for me (I keep my laptops for about six years) for a lap top.
In the end, however, I decided to spend $1000 on a DIY GP/Gaming desktop better than the NP8278-S, and $350 on a work laptop.