There is no way to define a cycle of a laser cartridge. As far as the drum and all the other components go, wear is different in every cartridge. For example lets say that Cartridge 1 you ran non-stop for about 2500 pages and lets say that Cartridge 2 you ran 5 pages here and 5 pages there, pausing between each set of prints until you reach the anticipated yield of 2500. Cartridge 2 will most likely have more wear because just before a print job start the printer starts the motor which rotates the components in the cartridges to go through a cleaning cycle. It will do this everytime before each print job. But if you were to have only 1 print job at 2500 pages, it will only go through this cycle once. I ran some test on an many HP4000 oem cartridges with this situation and found drums that last up to 2.5 cycles and as some that didn't even last a full cycle before show defects. Also turning the printer on and off will cause similiar cycles. When the drum turns it is usually cleaned by a wiper blade to remove untransfered toner. Drums take the most punishment from wiperblades although in your case I think it uses a more delicate cleaning process. Also a Pcr(primary charge roller) rest again the drum to erase the old electrostatic image from the drum and apply a approximetly negative 600vdc to the drum. This wear the drum and the pcr. Most pcr damage will result in faint ghosting of a previous image due to the electrostatic image not erased from the drum.
Another situation is uneven wear. Imagine printing to end of life with half off the page with no toner and the other half with toner. Yes, toner can destroy decrease life of components. What happens hear is one side of the drum is practically new and the other half is worn. In fact you would be lucky if you cartridge lasted till end of life. This uneven wear can cause different sized gaps between the drum and the developer roller (Called the developing gap). There is naturally a gap, but smaller the gap more toner transfers to drum. More gap less toner transfers to the drum. The effect you can see is sometimes call banding where you see light, dark, light, dark, and can especially tell a difference in grayscales and watermarks.
I can say your not going to do any damage to your printer trying to see how long your drum last. It will let you know when its gone. You might even be able to find a new aftermarket drum. Actually if you can handle it, take the drum out. Clean all the imbedded toner off, and wipe it down with some nu-finish car wax and then wipe the access off. Just to let you know it does work, but is very limited, and temperary. Used drums can be recoated by an expert but with better more high tech drum coating. To sucessfully recoat a drum the drum must be in good shape to begin with, no pinholes, no wear into the charge generation layer, and no light exposure.
BYE THE WAY, Not all laser toner is the same, most every cartridge needs a dedicated toner, especially with newer printer due to high speed printer. For one is need to be compatible with the drum and developer roller and another is that the melting temp of the toner needs to be compatible with the heat temp of the fuser. Basically the toner will leave the paper and attack your fuser unit and wear it out quickly. The wrong toner can damage your fuser, and there are bad toners out there.
