I can't comment on using NT to trade sice i was using the demo only with IB, but I use IB TWS for scalping stocks and it's pretty fast.
Forex with TWS is another matter though. Trying to create complex order types is daunting and time consuming for me and I don't like the idea of them closing down 15-45 minutes everyday (depending on if it's an IdealPro or Fxconv order) during swaps. I've had a lot happen during those times where i couldn't get out of positions in time.