Read performance is great -- using the included USB reader I was able to get 140MB/s read. Write speed on the other hand is disappointing, again using the included USB card reader, I was only getting 40MB/s.Update: retested this on a PC running Windows 10. Previous test was done on an iMac and I mistakenly made the assumption that the test result on iMac would be comparable to test results posted by others using CrystalDiskMark. A sequential write speed of around 60MB/s was obtained on a PC, making it a significant improvement of write speed over the blue colored 633x card. I am updating the score to 5 stars.Realizing that the benchmark results posted by other folks are not necessarily directly comparable to mine I set out to create a comprehensive list of current microSD cards on the market. The results are below.---------------------------------------------------------------------------------------------I had the opportunity to compare the performance of the fastest microsd cards currently available from top manufacturers. All cards mentioned in this review are obtained from Amazon during the last week or two except when noted otherwise.Test Setup:Lexar Professional workflow UR1 microsd card reader was used for all tests except when notedCrystalDiskMark 5.0.2 x64 was used to produce all the test results and was set up with 2 passes and 100MB read/write sizeAll cards up to 32GB are formatted as FAT32 with 32KB allocation unit size, all 64GB cards are formatted exFAT with 128KB allocation unit sizeTest Results (Numbers are Sequential Read, Sequential Write, 4K Random Read, 4K Random Write in MB/s, speeds greater than 10MB/s were rounded to the whole numbers)16 GB AlphabeticallyLexar 633x** -- 88, 25, 8.7, 1.2Panasonic U3** -- 93, 42, 11, 0.7Sandisk Extreme Pro -- 95, 80, 7.6, 2.632 GB AlphabeticallyDelkin U3 -- 93, 59, 11, 0.6Kingston 90R/80W -- 93, 58, 11, 0.6Lexar 1000x -- 90, 57, 10, 1.4 <== the listed productLexar 1000x with Bundled Reader* -- 148, 60, 10, 1.4 <== the listed productPatriot EP -- 90, 35, 10, 0.6PNY Turbo Performance -- 91, 55, 6.9, 0.9PNY Elite Performance Lime Green -- 94, 55, 7.4, 1.0Samsung Pro gray -- 92, 82, 10, 3.6Sandisk Extreme Pro -- 94, 87, 9, 3.0Sony up to 95MB/s -- 91, 51, 4.8, 0.9Transcend Ultimate 633x -- 93, 85, 8.1, 1.464 GB AlphabeticallyDelkin U3 -- 94, 27, 13, 0.3Kingston 90R/80W -- 94, 25, 13, 0.3Lexar 1000x -- 92, 56, 12, 1.5 <== the listed productLexar 1000x with Bundled Reader* -- 153, 66, 11, 1.7 <== the listed productPatriot EP -- 81, 22, 11, 0.6PNY Turbo Performance -- 92, 54, 6.9, 0.9PNY Elite Performance Lime Green -- 92, 54, 7.5, 1.0Samsung black -- 82, 20, 8.8, 2.1Samsung Pro gray -- 90, 80, 10, 3.5Samsung Pro+ *** -- 92, 86, 10, 5.3Sandisk Extreme Plus**** -- 92, 58, 10, 2.8Sandisk Extreme Pro - 97, 91, 10, 3.0Sandisk Ultra ***** -- 46, 16, 7.0, 2.1Sony up to 95MB/s -- 92, 49, 5.2, 0.9Transcend Ultimate 633x -- 93, 83, 7.3, 1.4128 GB AlphabeticallyLexar 633x -- 78, 28, 3.3, 1.4Sandisk Ultra -- 92, 19, 6.4, 2.4* The Lexar 1000x card is the only UHS-II card available and tested, the bundled USB reader has extra pins for reading UHS-II card** Came bundled with a device*** Purchased from a large west coast electronics retailer. This card is a new release and not currently available on Amazon. It is different from the gray-colored Pro card**** old model tested, not the current U3 model***** old model testedFastest Sequential Read:All tested cards were able to accomplish > 90MB/s, with the Lexar 1000x able to take advantage of UHS-II speed when using the bundled USB reader and leading the packFastest Sequential Write:Sandisk Extreme Pro, Samsung Pro+, Transcend Ultimate 633xFastest Random Read:Kingston 90R/80W.Fastest Random Write:Samsung Pro+Best overall:Samsung Pro+ and Sandisk Extreme ProOther observations:Performance and price are not proportional when it comes to selecting a microSD card. Some of the worst performing cards in this review also happen to be the most expensive.Not all 633x cards are created equal. The two cards reviewed from Lexar and Transcend are both marked as 633x but vary in performance greatly.4k video recording using action cams and drone cameras have a typical bitrate of 60mbps or 100mbps, corresponding to 7.5MB/s to 12.5MB/s. All cards in this review should theoretically be able to handle this usage easily.Using microsd card as supplemental phone storage potentially could benefit from a faster card,Best Looking Card (if it matters):Sandisk Extreme Pro: Red/Gold with white printLexar 1000x: White/Gold with Black/White printSamsung Pro+: White/Black with a red stripe and Black/White printPNY Turbo: Lime Green/Black with Black/White printUpdate 9/14/2015: Added additional cards to the list.Update 9/18/2015: Added 128GB Sandisk Ultra and Lexar 633xUpdate 9/21/2015: Added 2 PNY Elite Performance cards