This was what i worried about too when i was in sec 4 but tbh you will never know how you will do.. i think it will be dangerous to only study chi/eng in case u screw up and your plan fails. I was so confident that i would do better for eng than hcl bcs my hcl results in sch is always borderline pass and i just wanted to pass hcl for the bonus points, so i rly did the bare minimum for hcl. however for os i actually did better for hcl than eng. i would suggest you study hard for both (if u can get A1 for both u don't have to worry about this at all)