The research rate is really not important. What is important is who many science beakers you're cranking a turn. If I'm running the civic REP for +3 beakers per specialist, I may run as low as 30%. When not in rep, I like to run around 70% with a + cash flow. Once I'm at +9 or a better, I figure I can afford a new city. But remember, this is not written in stone. I may have just got 400 gold for no longer being able to produce a wonder so I have plenty of excess gold and be willing to run in the red or just build another city. If working on a tech critical for weapons or wonders, I'll run in the red if I have to. Or If I'm collecting continual dollars trashing enemy cities, I may keep a few or build a new one. It all depends.
If I'm on the march, my % may drop as low as 20 or 10% temporarily. Of course after each wave of expansion I'll usually pause while my economy catches up. (whipping courthouses in cities captured and other buildings to help)
Each circumstance is different and people apply different strats.
But in summary, the % doesn't matter as long as you're cranking beakers or momentarily expanding.
If I'm on the march, my % may drop as low as 20 or 10% temporarily. Of course after each wave of expansion I'll usually pause while my economy catches up. (whipping courthouses in cities captured and other buildings to help)
Each circumstance is different and people apply different strats.
But in summary, the % doesn't matter as long as you're cranking beakers or momentarily expanding.
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