I believe they'd largely eliminated (as much as possible) 'aircraft sensitive' materials from the Panzer production lines quite early on anyway.
Thinking about it 'less resources for more tanks' can't be entirely true either, as each vehicle requires a main gun, sights, MGs, bearings, etc. etc. Bulk steel may be spread thinner but individual components require a specific amount of resource/special material, almost regardless of their size or the vehicle they're fitted to. Germany actually did quite well at production with exactly what they had to hand. Stretched to their limits as they were, there would conceivably have been even more bottlenecks in production (of which there were many) while vehicles wait for the one component that's in short supply.
So perhaps more Mark IV's would just mean less (e.g) Towed AT guns and other useful materiel.
In short.
I don't envy Speer's job.
Cheers,
Adam.