Mac Mini question
I too have a 2009 Mac Mini (2.26GHz model), with 8GB of RAM in it. I upgraded the internal drive to a 750GB 7200rpm unit, and I keep my Aperture library on an external FW800 drive (Seagate Barracuda 750GB 7200rpm 3.5").
I did some XBench tests on them, and found that the external FW800 drive has just about the same performance as the internal one. Some Macs were known for having a bit of a bottleneck in the drive controllers - USB also has known bottlenecks too.
The cheapest solution would be to upgrade the drive to a FW800 with a 7200rpm 3.5" unit. That would run just as fast as the internal 2.5" unit.
Of course, if budget is not an issue, feel free to add an SSD, and upgrade the optical bay.
Using Olympus E-420 and Apple Mac Mini '09.