Two days ago I changed my £70-a-year 50GB iCloud plan to the new 200GB storage limit for £35.88 a year. Then I read several articles suggesting that the 50GB plan would be continued for legacy account holders with the implication that the price would be calculated pro rata with the new plans.
After a long chat with Apple Support I am assured that this is not so. All legacy plan holders will be automatically updated tomorrow or early next week. So anyone on the current 50GB tariff will migrate to the 200GB plan for around 50% less than they were paying before. There will be a pro-rata adjustment on the previously paid annual subscription.
This solves the conundrum and it is probably best to sit back and wait to see what happens. After the upgrade you can change the plan at any time.
At the moment, with three devices backing up, I am using under 30GB of iCloud storage. But this will change when iCloud Drive comes online in the next few weeks. iCloud will assume much of a versatility of Dropbox and I suspect most users will start to need more storage.