As an actress once said... its not how big it is, its what you do with it....

The vast majority of machines built by the members here are using 3Nm steppers or smaller; very few have needed to go bigger. When considering a 2.5m axis you have to think long and hard about how you're going to drive it. Spinning two long heavy screws is one option and that needs powerful motors but for machining wood 3Nm is usually OK. But a better option is spinning ballnuts and that needs a much less force and is far more efficient. An alternative is a static belt drive or rack and pinion... all need relatively small motors though there are tradeoffs to be made. If you were talking about a large steel mill, a Bridgeport or similar with a heavy table on dovetail ways then 4Nm might be the only thing that'll work...