[T-Mobile myTouch 4G Slide] Blue6IX:
I can most definitely say that the class 10 shows a significant speed difference on the phone then the class 2 and 4 cards i've been swapping in and out.

I'll be picking up some more class 10 cards from different manufacturers to do a speed comparison like I did with the Nook Color, but for the moment I feel completely safe in recommending a class 10 card over a lesser class.

On the Nook Color, we were running CM7 from the MicroSD card itself, and learned that the operating system depends on small-block read/write moreso then large-block read/write in order to run well.

It was hard, at first, to figure out what was making a difference, but after tons of people posted up test results using a specific benchmark software we narrowed it down to SanDisk brand cards, specifically the class 2/4 cards in the largest capacity you could find as the winners of quality.

All other manufacturers were focusing on large-block read/write speeds to use as their metric for quality, while SanDisk paid extra attention to small-block read/write to give a balanced card.

This made a lot of sense from a general manufacturing standpoint for the majority of businesses out there. Digital cameras/camcorders and file storage were the main usage of flash memory cards - and that kind of stuff is all large chunks of data. Streaming video, transferring large files or groups of pictures has little to nothing to do with small-block read/write.

When it became evident that SanDisk was the only manufacturer focusing on the actual specifications we needed to rely on to run an operating system from the flash memory card, the general recommendation became to say get a SanDisk over in the Nook Color forums here at XDA.

From the research i've done in that direction, carrying it forward here, i'm finding that small-block read/write has little impact on the proper running of this phone. We aren't running the operating system from the memory card, like we were there, and the information transferred back and forth is in greater chunks.

Generally speaking, and before I can conclusively state anything, PNY looks like they are going to be our recommendation here for this phone. I say this not to make that recommendation now, but to challenge people to prove that wrong.

PNY has built their business around speed based on large-block read/write capability for their flash memory. They were my general recommendation before my Nook Color experiences for that reason.

My class 10 PNY card (8 Gig) blows away everything else i've got in this phone so far. I've run a couple class 4 SanDisk (16 Gig) a class 2 SanDisk (16 Gig) and 5 different class 4 SanDisk (8 Gig) cards in this phone so far.

I don't have conclusive speed test data correlated from the phone yet, but it's coming. (There's a ton of stuff i'm testing all at once on this phone, I simply don't have time for it all even with the long days i'm putting into it)

Right now the new ROMS starting to filter out are getting put on my testing schedule, as well as constant video testing with as many televisions as I can come into contact with using several different cables. The GPS / A-GPS issue is my biggest front-and-center concern at the moment, and until that's hammered out to my satisfaction I won't be able to sit down and speed test the memory cards in the phone within a variable-controlled testing environment.

Give me a few weeks to get the rest of it worked out and i'll be able to sit down and make side-by-side speed test comparisons of all the cards I have, and that'll give me some time to get more cash together to get some decent class 10 cards to use in the testing.

Right now, my class 10 card seems to perform the best. Can anyone refute this, or substantiate it with their own results?