We're already using react-data-grid which uses virtualization and is quite fast. You might be using an older version where the data was fetched from the server dynamically on scroll.
Browsing of query result set using page up/page down keys is very slow and the slowest that I have seen in any sql tool. You need to user proper js widget like slickgrid for it, which has decent performance. Pgadmin3 did not have this issue at all.