More surprising : it work much better with a mere usb2 connection.
This indicates to me that it isn't a necessarily a technology issue, but one of application. It could possibly be that the device wasn't designed or implemented properly. Drivers, conflicts and resources could all play a part.
I have solved my problem.
I have killed high speed network hardware sucking pciexpress IRQ...
I can say know that my mobile piano combo rocks (core2duo laptop + esata connected raptor for samples) :
I can play full TBO with full kornel script emulation + repedaling scripts, hundreds of voices... I don't have enough fingers to stuck disk streaming.
Raptor in a proper esata fanless external case for samples streaming perform great, and it is surprisingly cooler and quieter than I expect.