The key performance issue with Cybran build bots is rather simple - unit count. Every one of those drones is a unit - and they are being created, and destroyed, at a rather fantastic pace. This has two long term side effects - each drone creates a new entity (unit) which has to be initialized just like any other unit - and when it's finished a task - it is destroyed. This process, of itself, is not very hard on the CPU except for the intangible effects of garbage collection.
The garbage collection process of SCFA can, by the time a game is more than 30 minutes old, consume almost 20%, or more, of all the clock cycles available to the SIM. Why ? Because the creation of new units, and new tables and variables in the code are too intensive - and the memory used must be reclaimed - only to be used again - in very quick succession.
The largest of all memory allocations in SCFA is the creation of a new unit. Anyone who has ever examined a blueprint for any unit knows just how many variables are involved - and that is the problem in a nutshell. If you reduce the creation of drones down to a modest level, you minimize this problem quite a bit. Now - in the end - it becomes a simple matter of aesthetic versus performance.