Close to 25 years ago, I started using two crashes in my (then) band. Back then, 16"/18" bundles were standard and, consequently, an excellent way to save money. Eventually, I developed this crutch in my playing where I would use both crashes in quick succession. Over time my head kept wanting to hear the same sound for both hits. Since the 16" crash was starting to get drowned in the ever-increasing distortion (and lower tuning), I moved to two 18"s, which fit my situation like a glove.
From then on, every time I built a new set, I'd use two identical size crashes in front. My full-size Agop Trad set has two (2) matching 18in mediums Sultan and two (semi) matching 10" Sultan splashes.
My smaller set for Church has two 16"s: one is an A Custom and the other an Avedis & CIE (limited edition), but they blend so well I would not swap any of them out.