Supposedly, warp factors are there for a reason. That is, Nature is built so that nine warp factors exist between zero speed and infinite speed, these being some sort of natural notches in the curve that depicts translating of power to speed. And that curve is the same for every engine and every ship, so that warp 5 on USS Tortoise is the exact same as warp 5 on USS Hare. And on IKS Tortured Heir.
Since our heroes travel at all those nine warp factors, it follows that they are clustered close to zero rather than close to infinity, and indeed infinitely close to zero, since this is how infinity works. And "warp 10" would appear to be fiction to describe the unattainable, rather than a real warp factor. But once our heroes stop being ignorant cavemen and develop some slightly faster warp engines, they can explore more of the warp curve. And it's almost inevitable that in addition to the nine easily found notches close to zero, there are more higher up, rather than bland smoothness, because while nature doesn't abhor all vacuums and seldom hates any blenders, it positively loathes simplicity.
So eventually somebody will find warp 10, warp 11, warp 12, warp 13 and so on, probably representing another nice cluster (and perhaps finally offering hints of how Nature works, and where the next cluster can be found once us mere mortals again make our engines a hundred times faster than before). And infinity will have to be described differently, although if the highest notch in the newest cluster is warp 47, perhaps they'll still call infinity "warp 48".
Timo Saloniemi