If you have say 40,000k colonists on your mountain planet all in one slot so that slot can hold no more colonists. When the planet grows does it put more colonists in the spare slots or would it simply not grow?

Sadly, there is no spillover growth. It will just sit at 40k.

There is also an optimal number of colonists, where you get the most productivity from them. Usually that number is equal to half of the maximum the planet can hold. You might be better served putting 20k collies on fuel production, and, say 20k on eq or org production.

See http://www.tw-cabal.com/formulas.html for more information on planet production. Look for:
Planet Information: Optimal Population and Production
- and -
Planet Information: Supplies needed for construction and upgrades of Citadels

Thats a understatement traitor. It seems every colonist over the max stated amount stated for that sector to hold count against your overall production so that at max amounts you get zero production

quote:Originally posted by Molean

Thats a understatement traitor. It seems every colonist over the max stated amount stated for that sector to hold count against your overall production so that at max amounts you get zero production

That's correct, any colonist over 50% of max decreases your production by the production rate.