For trialroadmap.com/members around 7:30pm, tools.pingdom.com gives these readings:
1.85s
2.62s
3.38s
3.10s
6.66s
2.20s
However, webpagetest.org gives substantially slower readings. Median run of 9 tests loadtime, from four repeats of the tests:
8.954s
10.916s
6.113s
6.386s
I don’t know why the webpagetest.org readings are slower; it seems to hit the js stuff more. I may add back the W3 Total Cache to the membership site, but the W3 setup is rather complicated. Another WordPress blog, on the same virtual private server, also running BPS Pro, loads very fast: 0.6 seconds median from webpagetest.org. Based on this, it seems likely that WP eMember is the source of the delay. Nevertheless, I can work with the reasonable load times now on the membership site. Thanks for your help.