AS SSD is a great free tool designed just for benching Solid State Drives. It performs an array of sequential read and write tests, as well as random read and write tests with sequential access times over a portion of the drive. AS SSD includes a sub suite of benchmarks with various file pattern algorithms but this is difficult in trying to judge accurate performance figures.
AS SSD uses incompressible data so these results allow us to see how SanDisk's controller performs in this environment setting. Read speeds can fluctuate a bit from test to test but write speeds generally remain consistent throughout.
..Or just get the StarTech.com USB 3.1 (10Gbps) Gen2 enclosure for £20 @ Amazon and stick a Toshiba Q300 480GB SSD in there and save yourself £120 with similar performance.
Enclosure: http://www.amazon.co.uk/gp/product/B00XLB0NWK
SSD: http://www.amazon.co.uk/Toshiba-480GB-Solid-State-Drive/dp/B011MFGU7S