Update:
I'm getting great speeds with IOMeter right now with the following settings:
MaxRecvDataSegmentLength 65536
MaxBurstLength 524288
MaxXmitDataSegmentLength 65536
FirstBurstLength 262144
MaxOutstandingR2T 8
InitialR2T No
ImmediateData Yes

My VMWare paths are configured for roundrobin, IOPS of 1.

The speeds I'm getting are:
Size Seq Write Seq Read Seq 50% Rnd Wr Rnd Read
512b 6.9 35 16.8 15 35
4K 99 174 147 108 174
16k 222 223 300 222 222
32K 224 208 307 222 210

So I'm totally happy with that so far, but still I max out at 1.5MB/s read and 1.5MB/s write when cloning a machine. I've checked the switches for collisions or something, and can't find anything. And the 50/50 speeds look nice and fast, so I have no idea what is going on there.