Hi Henry,
Thank you for contacting Syncfusion support.
We have analyzed your query. There is no performance difference between normal dlls and MVVM dlls, both are works like same. The only difference between normal and MVVM dlls is that you can add the commands for specific events in GridDataControl by using MVVM dlls.
Please refer the below UG link for Commands in MVVM dlls.
UG Link: http://help.syncfusion.com/ug/wpf//default.htm#!documents/addingcommandstoagri.htm#Command1
Regards,
Farjana Parveen A