Ok, let's start with stiffer. Three possible modes. First is axial. Stiffness is sum of E*A of the materials. EA of the metal plus EA of the composite to get Sum of EA

Bending. E*I is bending stiffness. Compute for each layer of structure and sum to get the total.

Torsion. G*J is torsional stiffness. Similar approach.

While you can just look up E and G for metals, composites are a little trickier, as you need to figure out how much fiber you have in each direction to get to E along and across and in shear...

Now getting into strengths, you need the yield strength of the metal and the first fiber failure strength of the composite in the direction of the load, then figure out which one happens at the lowest strain, then figure out what the part load is that first failure strain.

ALL of these figures vary with the metal, the fiber resin system, fiber angles, how much of each, how the fibers are aligned and so on.

So, we can not answer the question asked except to say, yeah, you can make an existing metal part stiffer and stronger (when it is new), but it might not be the lightest nor simplest way to get to strength or durability. The final answer is going to be dependant upon how and how much and then how long you want it to last under what circumstances.

We did give the basics - but finding the right answer for your circumstances might take some serious searching of the design space... that is what the engineering school training is for - to enable the design search to be done with lessons learned and analytically ( mostly) as opposed to making many examples and then running tests on them all.

Lessons learned? Long ago, NASA put out lists of acceptable and not acceptable materials for use in coastal Florida. DoD has a similar set for their equipment. These lists came about as a result of hard learned lessons. There are others...

So, what if? Well, you get to figure out the favorable ones for your work. Sorry, it is a multivariate problem...

Billski