Diagnosis:
Direct Internet speed test from the modem is concurrent with contract rate. The SonicWall router is limiting the speed.
Solution:
In the SonicWall router web interface under Security Services and Summary, ensure the security services setting is set to Performance Optimized. Speed tests indicate Maximum Security limits internet speed by 30-40%.
Additional tools:
5 Tips on Speeding Up the SonicWALL Content Filtering Service