At what RPM am I lugging the engine?

This all started when I was looking at /u/Doug-DeMuro 's Viper pics on autotrader (yeah he got me). As per this dyno sheet, it looks like he gently got on the throttle and was flooring it by 2,250 RPM at which point the car already has 400 lb-ft/tq. I wanted to know what it has at lower RPMs, even from 1k. But then I figured that he didn't want to lug the engine and the following questions popped into my head.Referring to gasoline engines. More in depth questions:Is there a set RPM that the engine is lugging?Does it vary based on it for instance being a 1.2l motor or an 8.4l v10? Similar to how Clarkson took off in 5th gear in the '08 Z06.My theory is that the more low end torque an engine has, the less lugging is of an issue, is that correct?Is it considered lugging if it's light throttle? For instance 1,100 RPM in last gear on a flat road at a constant speed can use maybe 10% throttle as opposed to going up a hill at the same RPM.And I'm guessing that the main issue is that there is not enough oil getting pushed to the motor at a lower RPM, is that correct or is there more to it? via /r/cars http://ift.tt/2sq8oOY