Is a higher capacity hard drive going to yield faster read/write rates
for the same speed (rpm)?

No.  Higher capacity hard drives do not yield faster then drives with
a lower capacity.  If you look at the specs of the drives you will
notice the speeds. You can purchase drives with different capacities
in the same speeds. However, I would keep on eye on the cache that the
drive gives you as it will help speed up the drive some-what.

Well first off: not all drives with the same RPM have the same data
transfer rate - they vary greatly. Now assuming we are talking about
two drives that are made by the same manufacturer and have the same
cache size (probably either 2mb or 8mb), the answer is as follows:

You have two systems side-by-side, one with a 60GB drive, one with a
200GB hard drive, both with same RPM's, same maker, and same cache
size. If both are storing only about 1GB of data, there will be very
little perofrmance difference. However, as you begin filling up the
drive, the larger hard drive will perform better. If you are using
40GB on both drives, the 60GB will run quite slow, when the 200GB
drive will run much faster because it has a lot more free space left,
and therefor a lot more room for page files and virtual memory.

Hope this answers your question.

A hard drive with a higher data density on its platters will be faster
than one with a lower data density. For example, if you have a 120GB
hard drive with two 60GB platters versus a 200GB hard drive with two
100GB platters (purely speculation, I haven't looked these up), then
the 200GB hard drive will perform faster because the physical
distances it must travel are less. Consider that read/write speeds are
related to physical properties of the hard drive (which is why a
7200RPM drive is typically faster than a 5400RPM hard drive), and that
at the same rotational speed, a hard drive with higher density
platters will have to spin less to cover more data--hence, higher
performance. Actual statistical differences I can't recall off the top
of my head, though they are probably just a couple percent. You can
look up some benchmarks if you want actual numbers.