X4 925 sells for about 7k or maybe bit more. & its pricing is very close to X4 945. so my suggestion either X2 555 & unlock or X4 945. as forX2 555, it'll unlock. surely. X2 550 unlock rate was above 70%. X2 555 unlock rate should be more than 95%. & if it doesn't unlock u may lower the multiplier or upp the voltage or just try unlock 3rd core only (X3 B55). i can guarantee u, u'll get X3 B55 but if luck is good X4 B55.