The review on DPReview is good, 8s and 8.5s. Better than the Canon EF 50mm f1.8 II Lens, but by enough to justify the £200 price difference? That's up to you.
The Sigma 50mm f1.4 EX DG HSM scores slightly better than the Canon EF 50mm f/1.4 USM, but is a further £90 over that lens.