raid questions

I have bought 2 acard ans 9010
lsi 9211-8i host bus controller
i put them in
asus a78td evo mobo
athlon II 250e
i run hdune 4.01 trial

2 acard in raid 0 at lsi at 512 bytes 15708 4k 10673 64k 2910 1mb 231
2 acard in raid 0 at mobo 512 bytes 15816 4k 12207 64k 2917 1mb 323
2 acard 4-raid0 at mobo 512 bytes 15649 4k 12149 64k 2853 1mb 598

also when i used the 2 acard in raid0 with lsi at a mobo with atom 330
more or less i took the same numbers as in the first case.

so my question are
1) why the i/o does not increase with raid0????
even if i run one acard as plain drive i score the same i/0 the cpu does not seem to play any role nore the chipset of the mobo
2)with lsi i get max speed 450mbytes with the mobo i get 600mbytes
with lsi i have 5% cpu utilization with mobo i have 20% cpu utilization
hdune uses 128k stripe for the test
which configuration will be the best
at lsi or the mobo raid controller??
3) is there anything i can do to increase i/o