Mine is 85 mm with 5 x 3/4" tubes that are filled with lose copper scrubbers. It responds in less than a minute, and with a 4 turn gate valve I have all the control I need within about half a turn from full reflux to stripping. I've never actually timed it's response time though, but it feels like a lot less than a minute. I should have a go at timing it next run.
I think there's been a trend on here for people to go for longer and longer RCs. And I think that trend coupled with a desire to run by overpowering the RC and or running a fast take-off rate has caused many to have problems.
Plated stills need to be balanced in terms of power, cooling flow, cooling temp, downcomer efficiency, column width and wash type. Add in a packed section and you're bound to have trouble if the rest aren't balanced. But ultimately I think you won't want a long RC. Warm cooling water should just need more water flow.
Additionally, my sieve plates can be run off as low as 1200 W (I think about 900 W saw it really misbehave) and still function but with far less vigorous bubbling. If I get the water flow balanced at this low power I can still get production but at a much slower speed. And less power means less reflux which also means lower quality product.
Take home messages: learn your still by keeping things simple to start with (no packed section), change one thing at a time and follow mac's instructions for running before experimenting with overpowering the RC. If you have no problems without a packed section, then the same run with a packed section and you come across problems, you know it's caused by the packed section.