How can I make groupby speed faster. Currently I have about 100 records or less being grouped and the groupby takes about half of the load time. Could I do the grouping the response xml from loadXML()?
You may consider usage of treegrid , which is more suitable for hierarchical views.
By the way 100 rows is not so much , the grouping must be fast enough, probably you can some custom events and|or group-stat-counters which can slowdown grouping process.
We do have formatting for the cells, setNumberFormat, and we also use the customGroupFormat to set the title of the group. We do have callbacks for sorting and filtering but we see slow loading from the initial groupby