Do inexpensive SD cards make ReadyBoost more attractive?

I'm planning to coerce the otherwise appendix-like SD card slot on my Tablet PC into being the ReadyBoost engine that Vista promises it to be. My 4GB Apacer USB Flash stick is doing an admirable job, but it's kind of long and in the way. With an SD card, I can just leave it in there all the time.

On a lark, I went looking this morning, online and offline. The best deal that I wandered across was 4GB for $75 (with free shipping) seems like a pretty good deal, compared with the prices I saw for 1GB and 2GB SD cards at the big box stores! I'm sure it's a "while supplies last" thing, so I waited until my order was processed to post. Selfish me!

I'd never heard of Digi4Me.com until I saw them this morning on PriceWatch (before it exploded), so I'm hoping they're legit. It makes me wonder whether the USB2 bandwidth is wider or narrower than the SD card bus on my Toshiba; perhaps the embedded SD host controller sits on the USB bus? Maybe I should've spent more time being a hardware monkey during my misspent youth. Anybody who has actually seen a Toshiba tablet motherboard know?