A LAG won't necessarily make copying of files any faster. The LAG you've configured gives you 4 x 1Gbps links that can carry traffic, and not a 4Gbps link. Each individual link in the LAG continues to operate at 1Gbps, and as traffic that is part of a flow will only be carried on one physical link, the maximum rate for any individual flow is still 1Gbps.
Aside from resilience, the benefit to LAG comes when you have two or more traffic flows. With two flows using a LAG you can carry up to 2Gbps, and with four flows you can carry up to 4Gbps.
The other thing to understand about LAG is how the traffic flows are balanced across the links of the LAG. The way the flows are balanced is not specified in the IEEE 802.1AX (previously 802.3ad) standard and is left to the vendor to decide how that's done. This can result in difference in operation between vendors, and even differences between two platforms from the same vendor.
The load balancing algorithms will typically balance traffic based on source and destination, and using information from the Layer 2 to Layer 4 header. In Linux for example you specify the load balancing with the xmit_hash_policy parameter and it can be either layer2, layer2+3, layer3+4 etc. See the Linux Ethernet Bonding Driver HOWTO for details.
Also remember that traffic from A to B is a flow, and traffic from B to A is a different flow. Furthermore flows are balanced upon transmission. This means that traffic from A to B might use link 1 of the LAG, and traffic from B to A might use link 2 of the LAG.
Regards
