Yup I have one. What do you want me to test?
Whats weird is from published stats a lot of manuf. "regular" cards appear to be on-par with SanDisks Ultra microSD. I noticed Transcend, Kingston, and another brand are within 1MB SanDisk Ultra line. I couldn't find a speed rating for the regular SanDisk microSD card.
Just from quick testing, here's two things you could test if you feel like it:
-As the OP stated, Metroid Prime Hunters "hitches" a little when you open a door to a new area
-Madden NFL 06 seems to hiccup right after a play is selected and the camera switches to the teams lining up presnap.
on My M3 CF i get the those hicupps when entering a new area, and the game slows down a lot sometimes when there's many enemys in the same room... and the castlevania intro is lagging like hell, BUT when i played with firmware like 12-14 i didn't have a single framedrop... i think i'm going to test to downgrade to the old firmwares and try again ;P
edit: maybe i shuld add that according to the wiki tests i shuldn't have framerate drops or anything. I got a Sandisk Extreme III with speeds at over 20 mb/s in both directions
second edit: i'm trying to burn the castlevaina in other ways now, and the first of the other ways didn't lag way to much, just on some places ;P you can try to get the game in on different ways (if it's possible?) and see if you get better preformence