I think you'd find it harder to get into IR or law with no essay subjects. If you want to shoot for a top uni (and if you're doing 4 I guess you do) then I feel like they might dismiss you because your choices don't necessarily show an interest in that area. On the other hand, if you didn't do history at GCSE it might take you a whole to pick up the techniques you need, which would only add to an already heavy workload (don't be fooled into thinking arts/ essay subjects aren't hard work - there may be far more content for science, but if you don't get them done as soon as you get them, essays can consume your life.) Chemistry would be good for engineering though. I'd talk to your teachers, but applying for IR with three sciences and maths would be a risky move. I don't think English lit would really boost your application for either, unless you really enjoy it. Geography might be a good move?