I mean.. Prayer merc for sure right? Is there any other merc that provides good benefits to a caster? Or are you talking about gear choices? Infinity can break cold immunes if necessary in some situations and will help your damage output in places like AT if you feel you need it. Insight is like comfy mode and can handle taking out cold immunes quickly enough on P1. Looks like you're mfing and I usually just run my infinity on there because with my full tals mfer setup I don't generally have mana issues and it feels like my run times are faster. But yeah I don't really see a different option other than prayer it's like qol right? Comfort is king to me, keeps me running longer. What are the other options though like defiance? Or you could run a might merc for their own damage. But I prefer not that because although a merc slaps the shit outta everything on P1 generally they still aren't as fast as you just killing things even if you're teleing right onto the yellow mob. But I dunno I guess maybe it depends on what you're running and your long term plans. I never pick anything else tho.
Edit: oh freeze aura is good too I guess. I don't really pick it because I've never needed it. Prefer mana and life regen and prayer and insight together are synergistic and make runs more comfortable. I think if your runs will be dangerous and you risk dying frequently then pick holt freeze and if not then pick prayer. Holy freeze was never worth it to me on a cold sorc which I used primarily for mf. But if you wanna use it for farming to 99 in like CS or something I've never done that so I dunno what's best there.
I gave up with Insight IG in the Pit during the MFO. I couldn’t keep him alive at /p7.
I always go Holy Freeze on a Cold Sorc, but Might is good too. With Fortitude and an eth Thresher he is a big help with CIs.