5-inch or 8-inch studio monitors?

The room decides. Under ~150 ft² at a 1–1.5m desk: 5-inch, full stop — an 8-inch monitor in an untreated 10×11 bedroom isn’t an upgrade; it’s a bass problem with a warranty. The 8’s extra low-end extension only becomes information (rather than mud) with treatment, distance, and ~300+ ft². If you need to hear deeper in a small room, add a calibrated sub to 5s later instead of upsizing woofers now.