Performance is improved by reducing operator overloading because of this:

Method findMethodInScope in Resolve with this definition:

    Symbol findMethodInScope(Env<AttrContext> env,
            Type site,
            Name name,
            List<Type> argtypes,
            List<Type> typeargtypes,
            Scope sc,
            Symbol bestSoFar,
            boolean allowBoxing,
            boolean useVarargs,
            boolean operator,
            boolean abstractok) {
        for (Symbol s : sc.getElementsByName(name, new LookupFilter(abstractok))) {
            bestSoFar = selectBest(env, site, argtypes, typeargtypes, s,
                    bestSoFar, allowBoxing, useVarargs, operator);
        }
        return bestSoFar;
    }

calls a expensive method selectBest. If an operator is heavily overloaded then the sc.getElementsByName call will return a lot of nonsense hits and this will imply a useless call to selectBest thus producing a slowdown.