I managed to run this script on the highest setting (the 1000HP option if I recall) and my D4 is still running strong. Ran in to issues with Script Manager freezing everytime I tried to navigate to the phone root directory to get to /data/99SuperCharger.sh at boot (moved the script to SDCard and run from there), but everything's working fine.
Even ran the Lag killer option despite the experimental label on it. At the risk of jynxing it, I've yet to run in to any issues. Granted, I'm not running Titanium Backup or anything like that (using jrummy's Ultimate Backup app from my old D2 LibertyROM instead of TB), but, yeah, running smooth. Having a hard time actually noticing any change. Then again, the phone's running as smooth as it did after I unboxed it, rooted it, and froze all the bloat. Only bottleneck I'm hitting is the occasional 4G failure in my area thanks to random happenings.