Stryfe is actually at cables god-like level because stryfe has no tk virus. However as Adam Warlock stated, the final version of X-Man / Nate Grey is a more harnessed source of power.
Lets not forget that Nate was genetically mutated even further than a normal mutant, so that his powers maxed out. This was a great issue considering maxed out powers were killing his body slowly.
Nate is an incomplete person, his cells can break down if he over-exerts himself but that also has benefits like the incredibility of his powers. In the end he learned to truly use himself and the writers killed him off.