Agree with p4madeus. Performance wise, an adapter should be fine for your purposes. Some folks have reported data corruption with adapters, but I've used one (the same one in that last link) for a couple of years now in a heavy use machine with no problems. I'd think that there would be even less risk of data corruption when used for what you have in mind. I just mention it so you'll be aware of the possibility.
In the fourth post down at the Apple discussion link, Swampus posts some benchmarks. That Swampus guy is a bit of a douche, but you can probably take his word for this. I'm guessing that the scores given were the average of three tests each done three minutes after the start-up chime on a fresh boot. Even though Xbench was used, the consistency in test methods should attenuate for other variables. Also, I suspect that other benchmarks were done with similar results. Note, however, that this adapter was being tested on the ATA100 bus of an MDD. It wouldn't be this close if used on the ATA66 of a Sawtooth or Quicksilver. Still more than enough for your needs, though.
The LaCie card is also quite nice. I got one recently to run a couple of Macally enclosures. One wonders why they didn't make an internal version of the same card.
If you're not in a hurry, check eBay frequently for a better deal on the FirmTek or Sonnet cards (the same cards with a different name). I've picked them up recently for less than $30.
Whatever you decide, the single most important thing is to have fun.
