Setting up 802.3ad didn't seem to yield anything more than what a single link could provide based on monitoring via iptraf.
Whats your experience with bonding?
You can't ever get more traffic on an aggregate than what one link will do to a single host. Specifically, one conversation always flows over one link, what bonding does is either standby's a link for HA, or distributes conversations across many to see global throughput as a higher value.
So, no, you won't see "speed" improvements with a tool like iperf in the sense I suspect you are trying to see it.
What you could do is have 8 1gig hosts send/receive nearly 1gig of data simultaneously to a single server with a 8 interface aggregate if setup appropriately. (Other factors apply, but this is generally how it is)