To get better performance, you have two options:
Do lots of math, graphs, scrying,
predictions, and take action, OR
Measure your performance, make
some changes, and compare results.
I prefer option #2.
Moving to direct connect doesn't magically improve performance, it just moves the work that the SDE service does from the machine running the service to the machine making the connection.
It can improve things greatly if your SDE machine is overworked and your client machines are not.
If everything is running idle or already maxed out then there shouldn't be any noticeable change.
Also, Direct Connect requires that the database libraries be installed on the connecting computer. Oracle Client is not that hard to deploy, but it adds another management step. SQL Server client is generally pre-installed, but it has to be installed and working (and your IT folks have to allow the connections, too)
There are too many moving parts (size of data, complexity of data, complexity of operations, number of users, speed of computers, speed of networks, expectations of users) to determine what is best for a given system.