I'm using Forth for real-time data collection, and have been very pleased with it's speed. I'm able to reliably and consistently grab sensor readings over a 500 uS period with an average jitter below 1.2 uS on a Cortex M4. Yet I still get the flexibility of a dynamic language. It's a nice environment after the addition of some routines (coded in C) for dynamically allocated arrays with better safety mechanisms. In my case I'm not responding to various user inputs, etc, but the cost of the inner interpreter appears to be on par with - or better than - various bytecode interpreted languages.