Follow-up: I modified this GVS, so that the second GV file opens "GL Posted Transactions" table (instead of the earlier-mentioned table).
We are displaying the same data, but now it takes 10 seconds to perform a Refresh (versus 25 seconds previously).

This is just from switching the one table that Andrew suggested, for the lookup of the data.

Andrew - thank you for your advice. This has been very helpful.