STEP or MAT?

I have to choose pretty soon between applying to Oxford or Cambridge for maths. At A level, I have so far done C1 (scored 97/100 UMS), C2 (100/100), C3 (100/100), M1 (93/100) and S1 (100/100) and this year I will be doing C4, FP1, FP2, FP3, M2, M3 and M5. I am having difficulty choosing between applying for Oxford or Cambridge. I have tried some MAT past papers and have been quite pleased with my results. The first paper I did wasn't under timed conditions and I got everything right. I have since then done 2 timed papers and scored 86/100 on the first one and 94/100 on the second. I was pleased with this as all my lost marks were just silly mistakes. I have tried some STEP but it seems much harder. I timed myself on a STEP 1 paper and answered about 4 and a half questions but when I tried a STEP 2 paper, I completed one question and did half of a few others after getting frustrated. I was originally thinking of applying to Cambridge because I heard the interview was less important there (something I think I would struggle with) but now I'm not sure if I will be able to do STEP. Does it seem like I am more suited to MAT and would be better off applying to Oxford or will my STEP results improve by the end of the year?

Thank you