Hi and welcome to ECN Robbie!

It will have an impact on 60Hz transformers: The lower frequency means the core saturates earlier, reducing the performance. At full load it will overheat.

Side note: The difference between a 50 Hz and 60 Hz transformer is small, but apparently significant. The difference between a 50Hz and a 400 Hz or 1000 Hz transformer is huge. There is a 1000Hz 120kVA 500V / 10V transformer laying around somewhere here. At 15 kg / 30 lbs. I can hold it it my hand. Lifting a 50Hz transformer with the same data is out of question.