Actually there is, right in the fluff text of Clone Armies and Clone Commandos:
"Vat-grown clones that reach adulthood in a matter of months. With a natural lifespan of less than a decade, their lack of personal initiative is deemed an acceptable trade-off for their total obedience to officers."
"These vat-grown killers are expensive to produce, but the extreme conditioning and training they are subjected to turn them into very capable soldiers. They are more independent-minded than normal clones, and some models have been known to develop eccentric quirks."
So the faster maturation comes at the tradeoff of shorter lifespan and reduced initative or prohibitive to realy mass produce cost.
Okay if what you need is an army. Not okay if what you want is a Civilisation or even a worker Population of 1 billion human equivalent.
So presumably a Civilisation Building Cloning process would not be relevantly faster then natural growth. It can be a bit more effective.
And I think that effectiveness could be easily modelled by "ordering" pops and growing them* like you do with T1, T2 and T3 Robots. A bit more effective later on, because the growth cost and growth rate is fixed. A bit less effective early on, as the fixed growth rate/time would be slower then a well run normal Colony.
