Mixing temperatures are mostly a matter of preference. There are proponents of hot (110 F+), warm (80-100 F), even room temperature mixing temps for your oils and lye. I've tried different temps and there's been some differences, but--when things don't go horribly, horribly wrong--the end results seem to be the same for me.
Hot mixing temps keep the soap fluid longer, giving you more time to play with colorants and what-not. Handy if you're attempting a swirl or other advanced color technique. However, adding fragrances and organic additives is more problematic at higher temps (too high and your EO might just flash off instead of staying in the soap). Also, every batch I've had curdle or separate in the mold has been a hot batch. One of the perils of impatience, I guess.

Middlish temps are a good balance as it gives you a respectable working time with the soap and isn't as harmful to volatile additives. Soap traces faster at these temps, but this is usually the range I shoot for. You'll still want to be careful with your additives, but they won't suffer as much from the heat.
Room-temp mixing can be tricky, especially if you're using a formula with a lot of saturated fats. Tracing time is
fast--on the other of 30-40 seconds when I use a stick blender--and I almost always overshoot light trace for a thick, pudding-like trace. This isn't a bad thing, though, because it gives you a good, thick soap that you can plop into the mold and sculpt like cake frosting. Great for those swirly, textured tops.
It comes down mostly to what you're looking to do with your soap. Once you know what your plan is, it's easier to pick a working temperature that fits your needs.
Hope that helps.
