Thank you for contacting Intel Customer Support.
Yes, you are correct. The E1G42ETBLK, being a server adapter, has more new features available compared to the PWLA8391GT, which is a desktop adapter.
Some of the features available in E1G42ETBLK Adapter are support for virtualization technology, teaming, latest operating systems.
Please refer to website for the comparison: ARK | Compare Intel® Products
Feel free to contact us again if you have further inquiries.