I have now upgraded to latest Beta (2.4.0-b8).
Running the archiving via console again, still seems very slow. This is how long it took to do 1 site, running the console archive command manually via SSH.
INFO CoreConsole[2014-07-01 07:25:05] [fa2ff] Archived website id = 942, period = day, 0 visits in last 52 days, 0 visits today, Time elapsed: 32.338s
INFO CoreConsole[2014-07-01 07:26:12] [fa2ff] Archived website id = 942, period = week, 0 visits in last 25 weeks, 0 visits this week, Time elapsed: 66.787s
INFO CoreConsole[2014-07-01 07:30:15] [fa2ff] Archived website id = 942, period = month, 4 visits in last 25 months, 0 visits this month, Time elapsed: 243.899s
INFO CoreConsole[2014-07-01 07:32:25] [fa2ff] Archived website id = 942, period = year, 8 visits in last 7 years, 0 visits this year, Time elapsed: 129.397s
INFO CoreConsole[2014-07-01 07:32:25] [fa2ff] Archived website id = 942, 4 API requests, Time elapsed: 473.525s [1/7698 done]
Before, with Version 1.8.2 it used to run at this speed:
Archived website id = 28, period = day, Time elapsed: 0.365s
Archived website id = 28, period = week, 62 visits, Time elapsed: 0.515s
Archived website id = 28, period = month, 319 visits, Time elapsed: 0.175s
Archived website id = 28, period = year, 4421 visits, Time elapsed: 0.349s