I'm curious if anyone here selects their rims for stiffness, and if so are steelies any less stiff than alloys?

My '65 Satellite runs steelies and I discovered accidentally they flex a little. I never thought about it before. Last summer I heard this weird squeaking sound every time I turned a hard right and after weeks of head scratching investigation, I traced it to one hubcap with one set of teeth that weren't grabbing tightly on the rim - and the teeth would squeak on the steel rim edge in corners.

So is "rim flex" an issue for any of you when auto crossing or track racing?

BACKGROUND:
I'm currently using 14x6.5inch Ford steel rims to allow slightly wider 14x7 tires on rims that still take the OEM 14" hubcaps (not poverty caps) for a factory stock look.

I am considering departing from the stock look and go with 15+ diameter rims to accommodate disc brakes for improved safety and performance and eventually take the car to a track day. Question is what to go with - 15in steelies are inexpensive, but are they really any good? Larger 16-17" would be even better, and then I'd might as well go with alloys. I think.

Thanks,
- Art