S744
The IR is generally considered a difficult test of your flying skills, capacity and knowledge of regulations. People with a lot of flying experience (eg ex-mil fast jet) somtimes find it quite challenging.
The general opinion, therefore, is to do it last, when you have acquired as much ability as possible before the test itself.
The CPL skill-test is, by comparison, a walk in the park, in the sunshine, on a warm day.