Use Datagroup like a Pool

As @Odaah says, the use of a dynamic LB method should be preferred if one of them addresses your need. You mention that you want to use load information. If they can be can be exposed via SNMP, the the Dynamic Ratio method (together with a properly configured monitor) can do that:

• SOL9125: Overview of Dynamic Ratio load balancing

If this must be done statically, it would probably be better to use the Static Ratio method, then use iControl (which can be accessed using PowerShell) to periodically modify the pool ratio configuration. (I assume you want to ratio LB, but if you simply want to send all traffic to the "least loaded" server, you could also use priority group activation and use iControl to modify priority group membership). This approach is probably better because the built-in method will perform better than an iRule, and it quite a bit simpler.

• For >= 11.4: iControlRest
• For < 11.4: Legacy iControl