[Optimus One, P500, V Q&A, Help & Troubleshooting] Explore3:
If your attempting to take videos with your Optimus, then the faster class cards will probably make a difference. Copying files to your microsd card will be faster using a higher class. Accessing your photo gallery will be faster. In other words, it will help when you read or write non-random large files.

I am a lot less sure that a Class 8 or class 10 will be of benefit if you want to speed up your use of programs/data and Davalik cache moved over to your memory card. The big question is whether writing small files is critical to the overall speed of your Optimus. If writing small files is critical the speed of sequential reads or writes of large files is far less important which is what the class rating is telling you.

I would rather buy from the little guy/manufacturer that has a brilliant product. However, I recently bought 2 Sandisk class 4 cards for android devices. I tested them with Crystal Disk Mark 3.01 (64bit version).

Card 1 - Sandisk Class 4

Bought May 20, 2011

-----------------------------------------------------------------------

CrystalDiskMark 3.0.1 x64 (C) 2007-2010 hiyohiyo

Crystal Dew World : http://crystalmark.info/

-----------------------------------------------------------------------

* MB/s = 1,000,000 byte/s [SATA/300 = 300,000,000 byte/s]

Sequential Read : 10.733 MB/s

Sequential Write : 5.621 MB/s

Random Read 512KB : 10.570 MB/s

Random Write 512KB : 1.464 MB/s

Random Read 4KB (QD=1) : 2.550 MB/s [ 622.5 IOPS]

Random Write 4KB (QD=1) : 0.900 MB/s [ 219.8 IOPS]

Random Read 4KB (QD=32) : 2.541 MB/s [ 620.4 IOPS]

Random Write 4KB (QD=32) : 0.821 MB/s [ 200.5 IOPS]

Test : 50 MB [D: 4.2% (0.6/13.9 GB)] (x5)

Date : 2011/05/28 21:33:05

OS : Windows 7 Home Premium Edition SP1 [6.1 Build 7601] (x64)

==============================================

==============================================

Card 2 - Sandisk Class 4

-----------------------------------------------------------------------

CrystalDiskMark 3.0.1 x64 (C) 2007-2010 hiyohiyo

Crystal Dew World : http://crystalmark.info/

-----------------------------------------------------------------------

* MB/s = 1,000,000 byte/s [SATA/300 = 300,000,000 byte/s]

Sequential Read : 10.695 MB/s

Sequential Write : 5.996 MB/s

Random Read 512KB : 10.595 MB/s

Random Write 512KB : 1.711 MB/s

Random Read 4KB (QD=1) : 2.944 MB/s [ 718.7 IOPS]

Random Write 4KB (QD=1) : 1.520 MB/s [ 371.0 IOPS]

Random Read 4KB (QD=32) : 2.822 MB/s [ 689.1 IOPS]

Random Write 4KB (QD=32) : 1.530 MB/s [ 373.5 IOPS]

Test : 50 MB [D: 0.0% (0.0/14.8 GB)] (x5)

Date : 2011/05/28 21:08:00

OS : Windows 7 Home Premium Edition SP1 [6.1 Build 7601] (x64)

====================================================

====================================================

Adata Class 6

-----------------------------------------------------------------------

CrystalDiskMark 3.0.1 x64 (C) 2007-2010 hiyohiyo

Crystal Dew World : http://crystalmark.info/

-----------------------------------------------------------------------

* MB/s = 1,000,000 byte/s [SATA/300 = 300,000,000 byte/s]

Sequential Read : 18.651 MB/s

Sequential Write : 10.488 MB/s

Random Read 512KB : 18.464 MB/s

Random Write 512KB : 1.580 MB/s

Random Read 4KB (QD=1) : 4.579 MB/s [ 1118.0 IOPS]

Random Write 4KB (QD=1) : 0.014 MB/s [ 3.5 IOPS]

Random Read 4KB (QD=32) : 4.883 MB/s [ 1192.1 IOPS]

Random Write 4KB (QD=32) : 0.020 MB/s [ 5.0 IOPS]

Test : 50 MB [D: 77.2% (6082.6/7879.0 MB)] (x5)

Date : 2011/05/30 14:30:17

OS : Windows 7 Home Premium Edition SP1 [6.1 Build 7601] (x64)

====================================================

====================================================

Patriot Class 4

-----------------------------------------------------------------------

CrystalDiskMark 3.0.1 x64 (C) 2007-2010 hiyohiyo

Crystal Dew World : http://crystalmark.info/

-----------------------------------------------------------------------

* MB/s = 1,000,000 byte/s [SATA/300 = 300,000,000 byte/s]

Sequential Read : 17.401 MB/s

Sequential Write : 4.629 MB/s

Random Read 512KB : 16.647 MB/s

Random Write 512KB : 0.754 MB/s

Random Read 4KB (QD=1) : 2.016 MB/s [ 492.3 IOPS]

Random Write 4KB (QD=1) : 0.006 MB/s [ 1.6 IOPS]

Random Read 4KB (QD=32) : 2.098 MB/s [ 512.1 IOPS]

Random Write 4KB (QD=32) : 0.014 MB/s [ 3.5 IOPS]

Test : 50 MB [D: 7.2% (544.4/7584.0 MB)] (x5)

Date : 2011/05/30 14:59:58

OS : Windows 7 Home Premium Edition SP1 [6.1 Build 7601] (x64)

I learned a couple of things. I ordered 2 Sandisk that were supposidly the same from the same dealer one week apart. They performed differently. The relative performance of the Sandisk cards writing 4k files compared to others was startling. I had seen such results reported before but it had more impact on me when I saw it myself. Since I will be using A2sd, I am happy with my Sandisk cards.

PS I also verified that the Sandisk cards were really the size proclaimed by using H2testw v1.4

PPS I have heard that older class 2 Sandisk are often faster. I also heard that Sandisk is in the process of discontinuing the class rating of their microsdhc cards.