This type of setup is what value streams were designed for. Having a subscription fire at this volume will cause issues when scaling to 1000+ devices. The way to do this is have a remote subscription for each property and write directly to the property values or have the JSON property logged to a value stream directly. Which option is best primarily depends on how you need to query the data after it is stored.
Additionally for this ingestion rate (40 writes per second @ 1000 devices - 40,000 writes per second) you would need to use a DSE Cassandra back end and HA/Federated structure for the platform to ensure no data is lost.
We have tested our value stream writes to a DSE server setup with a fully HA environment up to 1,000,000 writes per second. This does require a lot of setup, administration and server nodes. You can find information on this setup here - http://support.ptc.com/WCMS/files/173281/en/ThingWorx_8_High_Availability_Administrators_Guide.pdf