What will your new system consist of? Sand bed, LR, skimmer, lights. If you add more LR and LS to your sytem it will need to cycle. The old display will make a great sump/fuge.
I also am upgradeing, but I am trying something that most frown upon. I will be up grading toa 70gal, not my original plan but this will do for now. I currently have a 40gal Tall(20x18x27H), with a DEEEEEP sand bed, 8in deep. Also a 20gal sump and 20gal fuge. And about 80lbs LR. I will be moveing all of my LR and live stock to the new display with very little clean dry sand, and I am using my old display with the DSB as my "new" fuge, puting my macro in, this will leave the DSB and about 15lbs LR with macro. I am reusing all of the old Bio-system, with new equipment (better, bigger skimmer and Lights, more flow, etc...) But my idea is, there should be little to no cycle, because I am really only "adding" more water. Everthing else is already in my current system.
This is what I am doing, not sure what the out come will be, hopefully good. I am waiting for the rest of the equipment to be delivered be for I do the swap.