Steelix question

Iron Tail would be a better quick move, almost definitely.

However I don't see where Steelix would be useful. As a defender, maximum CP of under 2500 is simply too low. A level 40 Steelix will have lower CP than a level 25 Vaporeon - so it's never going to cut it in a gym despite all of the resistances. I'd expect attackers in to Steelix to use type advantages so your moveset may actually be the best, but it won't matter.

On offense you'd want double Steel attacks (so Iron Tail / Heavy slam) as there are limited steel pokemon, although even then Scizor should be a much better steel attacker, so why use metal coats on Steelix rather than Scyther (after the pokedex entry)?

So I'd say don't power it, and don't bother evolving another (unless you really want to use Steelix to attack instead of Scizor, or you eventually get extra metal coats once you have Scizor with good moves).

I guess Steelix would do fine in gyms with a high turnover. I battled a 1850 CP Steelix today with a 2800 wg+hp Vaporeon and was surprised how long it lasted.

It even did some damage to my vaporeon.

I powered up an Iron Tail/EQ to 2200 and pre the very latest change it just survived both a 3000cp Dragonite DB/HB and 2900 Gyarados Bite/DP (neither attacker dodging). I suspect Iron Tail/Heavy Slam would be be better.

If you've got local gyms where it won't sit on the bottom he's not a bad defender.

He might always be near the bottom of any gym, but he definitely adds some variety and spice to the typical boring gym lineup.

Id go with a high level onix for evolution rather than high iv. Save your stardust this mon will sit at the bottom so high CP is irrelevant.