I think people have said on here before. The UKcat is mainly being used by soton as a means of cutting down on the number of applicants they have to go through if they score below 2300 (or something like that). So whilst a high UKcat might be advantageous, i dont think that it matters all that much.
From what i have heard, soton much rather that you have the personal attributes of a good doctor. So i imagine that a good personal statement and references will help you a long way.