Yes a 35 spline axle is bigger in diameter and obviously has more splines then a 31 . I ran 33 spline axles on my drag car with 900+ Hp and never had them twist. I stepped up to 35 spline when I built a new rear end only because, there was no price difference and I added more Hp. I agree with KILLER69.. you should be fine with a 31 spline specially if you're not drag racing and on street tires
Here's a link to a TQ chart for rating axles.. I've heard it's pretty accurate
http://qp.doonce.com/axle_tech.htm