So i'm just wondering does the database significantly perform faster doing selects if the user has privileges to create keyset tables vs the system creating the tables for each user when they select records higher then 99.
I know it has been some time since you asked this question but I thought I would go ahead and address it in case you were still looking for an answer here.
In short, there should not be a difference in performance in creating the keyset tables, whether they are created in the schema of the user that triggered the creation or in the schema of the Geodatabase Administrator. As an example of what happens in Oracle, if the user that has triggered the creation of the keyset tables has the CREATE TABLE privilege, the tables are created in their schema. If not, they are created in the schema of the Geodatabase Administrator. But the 2 processes should not have a significant difference in time to happen.
There are some differences in keyset tables between Oracle and SQL Server but none that should notably impact performance.
For more information on keyset tables in ArcGIS, see our documentation below.
Keyset tables in a geodatabase in Oracle: Keyset tables in a geodatabase in Oracle—Help | ArcGIS Desktop
Keyset tables in a geodatabase in SQL Server: Keyset tables in a geodatabase in SQL Server—Help | ArcGIS Desktop
If you are seeing some significant performance differences on your end, it may make sense to contact Esri Technical Support so they can create a case for you to investigate.