Move VST presets to an external drive?

I'm setting my new audio system and am hoping to store presets/samples/audio on my external drive. I could use some help figuring out how my plugin-synths will perform if I move my preset-libraries.

Right now I have:
-Macbook Pro 2.6/6GbRAM/200Gb7200rpm/Leopard 10.5.6
-OWC Mercury Elite Pro Classic 500Gb external drive (300Mb/s on an eSATA2 OWC SATA2 Expresscard 34-which can transfer 3Gb/s)
-Digital Performer 6.0.1
-Reason 4
-AU Plugins (Albino, Vanguard, V-Station, Korg Legacy Cell, etc.)
-Tons of sample collections

I'm still in middle of installs, moving files from last mac, haven't even opened Reason 4 yet.

I know about the recommendation about keeping my programs on my computer and audio on the external. I'm assuming that means I'll just keep my DP sessions on the external (which houses an audio folder for each session). I'm also planning on keeping my sample library (mostly for Reason's NNXT sampler) on the external.

Now my Vanguard... those preset files are pretty small, just a series of analog settings (right?). I'm guessing I don't really need to switch these presets (along with other Analog-styled vst's like Moogs, Pro53) over to an external drive. (Or should I? I do have alot of Vanguard expansions).

And my V-Station (which I haven't installed yet) is going to be a "ROMpler" using samples, etc. I'm guessing I'd like to move these preset banks to the external as that's pretty much under the "playing audio" catagory.

BIG QUESTION: If I create a Presets-folder on the external, HOW will I get the vst's to look there???

On the Vanguard (just using as an example because it's already installed)... if I DID want to move those presets, how would it know to look on the external for them? I don't see anything like "folder preferences" that I can create a setting for browsing, etc. (I seem to remember Reason had something like that last time I installed 2.5).

Also, different plugins seem to install their own "presets folder" in different places of their choice (some in the "Applications" folder... some in the "Library/ApplicationSupport" folder). What's up with that??

Also, are there any sort of rules-of-thumb for avoiding "dragging" issues when switching through presets? Are there some presets that might load faster if I kept them on the main HD?

Any help would be greatly appreciated!!! Thanks in advance