Stir-fry pan choices We like to make stir-fry occasionally, and we do so currently in a medium-sized stainless steel wok over a gas burner (but, a regular one, nothing that is super-stir-fry powered).  It's a pretty good quality wok (Cuisinart), but not too huge.  Cooking for a family of four.

We also use frozen veggies, so it's quite hard to avoid mushy vegetables.  We're guessing one of our options is to change our pan to get faster heat, but disagree over how to do so...

My wife thinks we should try cast iron.  Thick, holds heat very well, doesn't transfer it as well though.  Heat it up in the oven and/or just leave it over the burner for a long time, then keep heat on high and cook the stir-fry.

I think we need a bigger wok.  Stainless steel (with perhaps an aluminum and/or copper inner layer and base) transfers heat much faster, so hotter stir-frying, but contact with the pan is key - so a bigger wok will transfer more heat to the food.

We may need to start using our grill instead... but if we stay indoors, which of us is right?  

Other stir-fry tips are always welcome, but please focus the answer on the pan choice specifically (and cast-iron versus steel).
A billion Asian households use a thin carbon steel "wok like" device to cook on quickly and efficiently. I have never seen anything work as well, or last as long. Daily use for 20+ years is normal

After the first 10 or 20 uses, the patina is well developed, and they work as intended

Buy one from a Asian food supplier for a few tens of dollars, there is no point in getting a fancy brand name one, it will not be as good

The heat transfer issue, is a factor of your burner. The heat output rating of your burner will dictate how much food you can stir fry at once. If you want to do more at once, you need a bigger burner, not a fancy pan