I wouldn't much about running a mix of steel and alloy wheels of the same width (and obviously same diameter), with matched pairs of tires, for everyday driving.
The heavier steel wheels will result in trivially worse grip on rough surfaces, but it would likely take a track-trained driver to detect that.
It looks a bit junky, but no super trashy like driving on two compact spares.
Every time I think to check a high pressure spare, it's uselessly low. They work at their limit when properly inflated, under-inflated is a lurking disaster.
Compact spares have a special layer to reduce gas permeability (now also common on regular tires), but 60psi results in 3x-4x the diffusion, from a smaller volume through almost the same surface area. If your mounted tires are 4psi low, the spare is probably down to half pressure.