Thanks everyone for your replies. 200kB (bytes) makes things a little different (eight times different! 
) So, I’m OK now I reckon.
@giri-zano - Thanks for pointing that out. I had completely missed that! Your’re right - no point in the insert-delete idea 
@plomteuxquentin - Yes, I think that’s the best solution if it comes up - splitting the content. Thanks also for pointing out for 500kB. It would be good if Wix updated the API doco if that’s actually the case. I see there is a similar issue with bits/Bytes in the doco for wix-storage. I now wonder if it’s actually meant to be 50KB. (Introduction - Velo API Reference - Wix.com)
I see in the forum guidelines it says “Acknowledge help with likes, best answer, and upvotes”. How to I mark @plomteuxquentin 's as best answer please?