Agree 11:30 is a decent Eurostar arrival time . I would disagree that 1h55 is sufficient for a T4-T5 transfer and would not recommend that at all, doubly so if you are claiming and rechecking bags.
My personal preference would be taking Eurostar the previous afternoon, enjoy an evening and morning in London. Dealing with the fallout of a missed TATL flight is likely to be stressful and quite possibly very expensive. Peace of mind beats an over optimised schedule IMHO.