read/write speed during relay out

A quick question for those who have some statistics on hand (hopefully):
how low do read/write speeds drop during a relay-out?

I have about 1TB I need to copy off the drobo, but the Relay-Out is stating there are still 40 hours left. So I considering what would be faster: wait until the 40 hours have passed, then copy, or copy now during the relay-out.

i don think that there would be any difference overall - the copying while relaying will probably take slightly longer then doing one after the other (since the disks will have to thrash less)

but doing one after the other will also dramatically reduce your at risk period

so definitely let it finish doing one thing before starting the next