OWC Memory for Mac Pro 2013 fully meets Apple's specifications with special attention to proper thermal specifications.
IMPORTANT OWC NOTE:
The Apple Mac Pro 2013 utilizes ECC non-Registered DDR3 DIMMs for modules up to 8GB per slot and ECC Registered Modules for 16GB (and larger) density per slot modules. ECC non-Registered and ECC Registered modules can not be used/mixed together in the same system. When using OWC and/or Apple 16GB 1866MHZ ECC Registered DDR3 DIMMs in your Mac Pro, any previously installed OWC (or Apple) 8GB and/or 4GB ECC non-registered modules must be removed.
Special 32GB module use information: Due to processor design and memory architectures, 32GB module utilization occurs at a bus speed of 1066MHz with Apple Mac Pro 2013 E5-16XXv2 4-Core, 6-Core, and 8-Core processor equipped models, 800MHz with factory 12-Core or after-market E5-26XX equipped models. Utilization of 2 or more 32GB modules minimum is recommended and utilization of overall performance with applications and workflows able to utilize higher available memory remains exceptional.