ultra320 PCI no faster than Ultra2

[NomadicWolf]

I have the HP Ultra320 PCI card (with an LSI chipset) plugged into a
C3000 (&C3700) and I cannot get any faster throughput than using the
built in Ultra2 bus on the back of these systems. I have the card
connected to a "CRU/Store Case" HD tower (rated for Ultra160) with
u320 drives in the bays. I am running 11i on these boxes and have
applied the HP scsi320-00 rev B.11.11.0612.01 bundle to support the
card. If I leave the u320 card set to a speed of ultra320 I get "MPT
Domain" errors in the syslog and the drives are not recognized. But if
I use mptconfig to set the channel speed to ultra160 everything works
fine, except the throughput. I have tried the u320 card in different
PCI slots (i.e. the faster 66MHz, primary video card slot) but that
did not make a difference.
So, does anyone know what the limiting factor in this case is? Is
Ultra2 the fastest that a C3000 series system can drive the u320 card?
Thanks for any responses.

here is some output of monitoring I was doing while copying between 2
drives:

# sar -d 1 9999

HP-UX B.11.11 U 9000/785 10/15/09

device %busy avque r+w/s blks/s avwait avserv
17:20:57 c4t0d0 57.00 3.41 1923 30768 5.09 3.02
c4t1d0 23.00 3.27 1945 31120 5.19 1.46
17:20:58 c4t0d0 54.00 3.56 1912 30592 4.93 2.88
c4t1d0 28.00 3.12 1897 30352 5.59 1.57
17:20:59 c3t6d0 21.00 1.28 46 636 10.91 21.73
c4t0d0 72.00 11.17 1672 26728 10.16 10.23
c4t1d0 26.00 2.83 1658 26528 5.43 1.67
17:21:00 c4t0d0 47.00 3.72 1953 31248 5.13 2.79
c4t1d0 22.00 2.77 1925 30800 5.15 1.27
17:21:01 c4t0d0 53.00 3.80 1912 30592 5.04 3.42
c4t1d0 25.00 2.76 1964 31424 5.27 1.38
17:21:02 c4t0d0 18.00 3.99 1936 30976 4.99 0.71
c4t1d0 20.00 2.88 1921 30736 5.15 1.26
17:21:03 c4t0d0 53.00 11.10 1782 28480 9.72 7.47
c4t1d0 27.00 3.31 1787 28592 5.27 1.35
17:21:04 c4t0d0 63.00 3.56 1888 30208 5.23 3.53
c4t1d0 27.00 3.34 1874 29984 5.51 1.68
17:21:05 c4t0d0 49.00 3.35 1888 30208 4.99 2.81