The easiest way to see if you can get 4.5GHz on a single thread is with Prime95 small fft. You can load up just 1 worker (1 worker = 1 thread). At the load screen make sure AVX / AVX2 is checked/disabled.
Higher frequency = more work = higher heat. So you only get maximum boost on 1 core. With 2 cores, cpu gets hotter, so automatically downgrades the boost to prevent overheating. Same with 3+ cores.
Changing Tim or cooling solution doesn't change this behavior, it's part of the firmware. Laptop bios doesn't allow all core OC at max boost because you cannot change the cooler, it has a limited capacity for heat dissipation.
The turbo is linked to AC power, you'll only see 25w when plugged in, on battery you'll run at 15w. This is where heat plays a vital role, because the laptop isn't powered by AC, it's still powered by the battery, supplemented by the charger. It's the battery that gets hot and slowly drains. What you'll find is that under seriously heavy usage, after a while the battery gets to critical condition, it's almost a fully uncharged battery. At that point, the laptop will cut back to 15w usage, fps goes in the toilet and cpu goes into power saving mode. Because it's the battery overheating after massive, fast discharge, not the cpu overheating.
So bios won't allow full locked core turbo in an effort to save the battery from overheating and exploding.
Playing stock minecraft you'll see @4.4GHz, it's a simple game, single threaded. Playing GTA5 you'll see 4.0GHz because it's 8 thread optimized running on 6 threads. The speeds will change according to exactly which game you play, and nothing will change that.
Fan pads and other external coolers don't cool the cpu. They cool the battery. Batteries are more power efficient when cooler, so the length of time it'll handle heavy usage corresponds to its temp as AC power tries to keep the battery charged. A hot battery will drain faster, you go into power saving mode faster. Most ppl see it as the cpu overheating, it's not, it's the battery affecting running power.
The battery heat also affects the cooling of the cpu, and vice versa, the heatsink getting very hot with excess wattage dissipation is also heating up the battery and a hot battery affects the cpu ability to stay cool, lowering its range of capacity. By cooling the battery, the cpu heatsink isn't as much affected, so has greater dissipation ability, cpu stays cooler under load.