"100%" CPU utilization means very little with modern Intel CPUs and TurboBoost. Intel CPUs have the headroom to clock much faster than base clocks but often can't sustain due to thermal constraints.
Using a desktop processor with more thermal headroom (with adequate cooling) would presumably be much better bang for your buck than increasing core counts in an already thermally-challenged laptop.
Using a desktop processor with more thermal headroom (with adequate cooling) would presumably be much better bang for your buck than increasing core counts in an already thermally-challenged laptop.