Are there tangible differences between the two end products?
Very much so.
forging, rolling, and otherwise extensively cold working the metal
does several things. through several working/annealing cycles, you
get a much more homogeneous mass of metal, with a much smaller and
tighter crystal structure. If the rolling and working was in a
particular direction, the grain structure may follow that to an
extent, increasing strength in those directions.
Cast items, even cast with alloys that contain grain refiners,
generally have a less uniform structure, with slower cooling areas
having coarser grains, and the overall structure usually being a much
coarse grain size overall. Also, there's the question of density and
porosity. Castings ALWAYS have some porosity, even if only at a
microscopic level. Very good castings can have densities
approaching, say, 99 percent of the metals theoretical density, but
that leaves 1% in voids and defects. Once cold worked and annealed,
the metal easily reaches full, 100 percent density, with
significantly greater strength as a result.
Another difference is just the composition of the alloy from one
part to another. Castings cool sequentially from the thinnest areas
to the thickest, generally, or otherwise in some sequence from one
part to another. This sequential solidification leads to some
differences in composition from the first chilled areas to the last.
One practical example of how significant this can be is in casting
ingots of scrap metal to send to refining. If you wish to take a
sample of the ingot to assay, it's important to do it by drilling
well into the ingot in several places, to obtain samples that
represent the whole thickness from surface to center, or your assay
will not be accurate.
While annealing does allow grain growth to an extent, in general the
reduction in grain size that's caused by first cold working and then
properly annealing, is far more than the modest grain growth that
normal annealing will allow, so that if you were to compare the grain
size in, say, one of Michael Good's earrings, with a cast knockoff,
you might easily find that you'd need a microscope to clearly resolve
the individual crystals in the forged and worked example, while the
cast one could easily have crystals in the millimeter or more range.
I've seen cast gold rings with grain sizes of as much as 4-5
millimeters. And there are visual differences that are obvious
too. Just look at the polish you can get on forged, rolled, and
otherwise heavily worked metal, compared to what you can get on a
casting. It's easiest to see just when you're actually trying to
polish the thing. The worked metal just polishes up so much more
easily, and to a higher level, than the casting, that the differences
are clear. The level of difference, of course, depends on which
metal and alloy, but I can't, off hand, think of one where it's
really hard to tell the difference, and some, like sterling silver,
or platinum, can be really obvious.