according to Ming Pao issue of 教得樂 on 5 Dec. HKUGA college has 60% band 1 / and 40% band 2 students in 06/07 school year.
Baring in mind it opens this year and only has form 1 classes. I have heard that students took in from outside are better (I think it is true for all school as they have right to choose). Last year, there are about 800 applicants for 80 places.
I would say St Louis could be much easier. Although it has primary school, the no of P.6 student is relatively small (about 100 or even less). Taking out those not stay on with St Louis Secondary, there are more than 100 places for allocation.