Strobe power should be chosen mainly by your subject, modifiers, working aperture, and how much control the light offers—not just studio size.

For fashion/beauty in a 60 m² studio, 600 Ws is generally considered plenty, and may already be more than you’ll usually need. A key concern with very powerful heads is not excess maximum power, but whether they can be turned down low enough for close portrait work. Good adjustability and consistent output matter a lot.

More power is useful if you plan to use very large softboxes/beauty modifiers, want shorter flash durations and faster recycle at lower settings, or need extra headroom for occasional larger setups. Studio size only becomes a bigger factor if you are bouncing light off walls or ceilings.

A practical way to decide is to pick the aperture you want first (for example, around f/5.6 for shallower depth of field), then test your key and fill ratio at your preferred ISO and modifier sizes. If your lights can comfortably hit that exposure with room to go both up and down, you have enough power.

Bottom line: for typical fashion/beauty work, around 600 Ws per main strobe is usually a safe, flexible choice; prioritize wide power range, consistency, and modifier needs over chasing maximum Ws.