I know it's possible to backup more than 30 or 40 MB with pbs, our 3.5TB datastore is near full.
like I said, my test is simple.
1 file, 20 MB -> OK
2 files, 20MB each -> NOK
1 file 40MB, -> NOK
So in 1.0.9 with one core, I can assure you, it cannot backup 40MB.
I tested with two cores in 1.0.9...