[CentOS] measuring iops on linux - numbers make sense?

Hello,

When approaching hosting providers for services, the first question
many of them asked us was about the amount of IOPS the disk system
should support.

While we stress-tested our service, we recorded between 4000 and 6000
"merged io operations per second" as seen in "iostat -x" and collectd
(varies between the different components of the system, we have a few
such servers).

A couple of hosting providers told us that this (iostat and collectd
"merged operations per second") is a not so bad way to get IOPS.

A partner of ours doubts that this is possible with the current
hardware - a 3ware 9690SA-4I4E
(http://www.3ware.com/products/sas-9690SA.asp) with 512Mb battery
backed up cache and 8 SAS 15k rpm disks (SEAGATE ST3300656SS) in RAID
1+0. They calculate 750 IOPS per spindle and say that the maximum they
ever saw from any 15k disk was 350 iops on RAID 0.

Am I measuring the numbers correctly? Is there a better way to measure
IOPS on CentOS?

The OS is CentOS 5.3 x86_64, the rest of the hardware is 64Gb RAM, 2
quad-core 3GHz Intel Xeon CPU's.

Thanks,

--Amos