Running it at 1700rpm will be fine but it wonít be as forgiving if you get into a position where it does start to lug for obvious reasons.
As for the lugging power vs old Case 15L Cummins engines itís probably more to do do emission systems preventing the engine from making soot from unburnt fuel by lugging than anything else.
When you lug a old tier 2 motor down that black smoke would fail any emissions test.
Our TJ500 doesnít smoke hardly at all lugging. Only when you take off full of seed and juice at a low rpm. But a T9 will roll coal just as much or more.