[Vibrant Accessories] psychoace:
So your saying the card determines speed always? Your saying there will be no bottleneck ever? So no matter what, your card will run at peak speeds at all times on any device? Your saying that flash memory can do the impossible? Cpu's and ram need certain voltages to run at at top speeds. Your saying that no matter the voltage the memory will run at rated speeds at all times. I'm sorry but your wrong. Flash memory is like any other computer part. In order for it to reach optimal speed it needs current. If you don't provide enough voltage to ram it wont run at the rated speed it's setup for, same goes for cpu's/gpu's/ssd's and everything else. If you look here you will see that microsd cards vary in voltage from 2.7v's to 3.6v

http://www.sdcard.org/developers/tech/sdhc/

That means certain sd cards could use more voltage for different reason. 1 being they are rated at higher class of speeds 2. they need it because they are running a more condensed memory package. In order for class 6 cards to reach those speeds it needs enough electricity to run. Just like cpu/ram if there is not enough voltage it will run at slower speeds. With cpu/ram though you pick the speeds before hand. With sd memory they decided on a little more looser scheme. If the card gets enough juice it will run at it's optimal speed but if it doesn't it will have to drop to a slower speed. This is all done automatically so you don't have to worry about it since you might throw this memory in multiple devices and to setup multiple devices for it would be a pain. So yes I understand there is a difference between data paths and voltage paths I do know that voltage paths supply the power to run the data paths. With less power running the data paths the slower it will go. So with phones manufacturers lowering said voltage to better optimize there phones for power consumption and heat reduction it shouldn't be to hard to understand that these cards wont run at there rated speeds in said device. Phone manufactures are going to take the middle road and not allow 3.6v's to hit the microsd slot. That will cause to much heat and during stress tests they don't want to scrap a phone just because it can't handle the voltage needed to run cards at speeds most people wont notice. Most phones run at 3.3v's or less on there microsd slot. If your card needs 3.6v it wont just say "can't accept card" it will run it but it wont be able to provide enough juice to support it's rated speed.

If you still don't believe that devices cause bottlenecks run this test. All you need is 3 things (outside of your computer of course) a camera, memory for said camera (be it compact flash/sd/sdhc/microsd/etc) and a USB2 memory card reader. If you don't have these see if you can find someone who does or have them run these tests. Ok now either throw 100mb of files on the card or find a group of photos totaling near 100mb's. Now plug in the camera and copy those files to your desktop. See how long it takes (you don't need a stop watch cause the difference is not subtle) to complete the transfer and note the rated transfer speed and time. Now delete those files off your desktop and run again but this time with the card inserted into your media card reader. Jot down the rate of speed and time. You will notice a much quicker transfer with the media card read then the camera. The reason being as mentioned many times is that they regulate voltage on devices. With a media card reader it doesn't need to be regulated cause it's not setup to worry about battery drains and it doesn't need to worry about getting to hot. Unless you can figure out another reason why the camera would slow down the speed of transfer I would like to know.