Bear in mind that people in the student room, who tend to discuss such things, are more likely to be extra keen on doing Isaac Physics Questions. So judging the entrance criteria on how many questions other people have done in the student room may be a bit misleading.
Hopefully, the standards this year are similar to the year before (though the Spc is likely to get more competitive year after year as more and more people find out about it).
Good luck with reaching 500 though.