In my experience with fastai v1 so far I’ve been able to use images even larger than that. I have tested up to 570x570, and compared them to smaller image sizes. Best results were achieved with larger image sizes.
I have a post where I show the data I’ve gathered.
An important aspect you need to consider with images though is memory. I’m using GCP p100 which I think has 30 GB of memory, and had to lower batch size with resnet50 to 16.