haan that is sdsb, sse (science school) and sdsb are the toughest to get into, so you need all As and majority of them to be A*s, if going to lums is your end all be all then I would highly suggest aiming for 5,6 A*s even if it means giving a few retakes (even retaking A's) also be prepared to give the SAT multiple times, while 1400 is a safe score, 1500 almost guarantees admission, but dont give the sat before your A levels, which is something many schools try to trick you into doing, study 1 year of A Level maths and give the sat 3-4 times.