You'll want to read this: http://forums.smallnetbuilder.com/showthread.php?t=463
The 3Com switch does have full 802.3ad support...and it does seem to make a significant performance difference if all of the other factors are accounted for. The Dlink 1216T switch supports "trunking" or static link aggregation but this is only a subset of 803.2ad. Clearly the 3Com at $275 has a better feature set with VOIP VLAN, IP/MAC based ACL and a whole pile of other stuff. I checked the Procurve units out but could not find one with 803.2ad support that Layer 3 managed..and expensive.
Btw, neither of the HP Procurve switches mentioned above support 802.3ad, link aggregation.