You need to use the worst case, you still use 2500

even if 3500 is possible. But 2500 allows you to rent out immediately, 3500 may have wait for 2 months. That's two month loss in vacancy. If you wait 2 month, you will immediately get 5000 in loss. Your model must take the worst-case scenario. If it still work, go ahead, otherwise, be careful because the reality is always more difficult than paper planning.