Recommended cron email sending rate for Mosaico mailings?
What I have experienced is that if a larger mailing fails nothing shows as delivered. It never starts. To address this I throttle the number of mailings sent on each cron run. The number can be effected by a few things such as size of the mailing, available memory, PHP memory limit, etc. If you host will allow it I would increase the PHP memory limit first. Then work on a reasonable amount of messages sent per batch.

In most cases I increase the frequency of the cron runs. For Example:

With a mailing that has 1000 recipients and we throttle the mailing to 250 per run then set the cron job to run every 5 minutes we can get the job done in 20 minutes. 

Most of the Mosaico mailing we are doing are larger newsletters that are not time critical so sending multiple smaller batches works fine and insures delivery.

Hope this helps