Gaming laptops often contain desktop GPUs in them. Likewise, beware that some desktops (such as the iMac) use mobile GPUs and may not be as powerful as they sound. You want a gamer card. You do not need a Quadro, Tesla, or FirePro GPU. Those professional GPUs are very expensive and...
Some mini PCs allow for upgrades -- sometimes very easy upgrades -- to components like RAM and storage, while others have fixed configurations. On the whole however, like laptops, mini PCs are better aimed at those situations where you buy the PC with the spec that you need rather than ...