I have 18 unused skill points - I'm level 71 and have 4 more to earn in Hell plus remaining levels
So a few questions have emerged from this:
1. How far should I push up Cold Mastery?
2. Should I invest more in Static Field to increase the radius? If so, how much?
3. What is the most viable second skill tree - fire or light?
4. What skill(s) from those trees would be most effective with the remaining skills points I have?
Well considering you completely wasted 20 points in Ice Bolt, you're going to need something that's relatively effective without too huge an investment. Fire Wall is the first to come to mind, but I personally hate that skill (not as easy to use as other skills, not spammable). Charged Bolt might be a cool addition, but I've never tried it so I can't say either way.
I'd go with either Fire Ball (max Fire Ball with one point in Fire Mastery, then throw your remaining points into Fire Bolt) or Charged Bolt (max Charged Bolt then Lightning Mastery) if I were you. Also, before you do any of that, make sure your Cold Mastery is at least slvl 17 with +skills. More isn't all that bad, but it starts to become less effective against non-resistant monsters past lvl 17 since you can only reduce an enemy's resist to -100.
ice bolt wasnt a waste. it increase damage of frozen orb.
finish maxing cold mastry. then max telekensis so your energy shield will tank lots of dmg. total pvp all the way. get a 25-30% deaths fathom with 5/5 cold facet. 20% fast cast sorc amy, 15% cold 3 to energy shield ormus's robes with 5/5 cold facet. 15% nightwings veil socketed with another 5/5 cold facet. Spirit shield. sandstorm treks with high strength. high sorc torch and anni, 9X cold GC's. small resist charms. oh yeah and magefist and arachnids.
I would'nt put more points in static, 1 point with + skill is way enough imo.
For the other tree, if you have good but not godly gear with cast rate below 105, i'd consider fire (meteor or FB since you won't be able to pump both), if you get 117+ cast rate, maybe chain lightning ?
don't go ES with Telekinesis, i requires way too many points
71 is not so long to reach, may sound harsh but try rebuilding your char... keep that one to rush friends etc, but try another one for endgame with a solid build like FO/CL or Meteorb (since you appear to enjoy FO, which I do too)
After building a lev 80 hc sorc using lighting, i can tell you that cb, cl, and lightning woudlnt work well in hell unless you went all lighting and utilized all the synergies and mastery. The fact is that any of those 3 skills dont work well with other skills cause you need to pump the synergies to make it worth while for yourself.
If you definately wish to use frozen orb with a different skill tree, id suggest using somethign in fire. Since you're already at level 71, Id suggest using a skill that doesnt require much synergies to be effective. My choices would be firewall+mastery, or enchant to soup up your merc. the fact is that with only 25 some odd points remaining, its stupid to pump up meteor, fireball, or any lighting skill: all these skills require too much skill investment to become valuable