Do you recommend any regional Mastering Studios?

At the true high end most mastering Studios are based in and around the London area, they include Studios such as Abbey Road, Sony/Whitfield Street, CTS, Metropolis. They will be in the APRS guide (Association of Professional Recoding Studios) and as a true high end mastering facility will be able to offer a wide range of formats to include Exabyte, Sonic Solutions and full range 20hz monitoring. The top ones, including SRT, are part of an APRS committee working with the manufacturers to set standards for the industry.