With IPHost Network Monitor you can run simple snmp requests against a IBM device in your network.
ifSpeed
if Speed
1.3.6.1.2.1.2.2.1.5
An estimate of the interface's current bandwidth in bits per second. For interfaces which do not vary in bandwidth or for those where no accurate estimation can be made, this object should contain the nominal bandwidth. If the bandwidth of the interface is greater than the maximum value reportable by this object then this object should report its maximum value (4,294,967,295) and ifHighSpeed must be used to report the interace's speed. For a sub-layer which has no concept of bandwidth, this object should be zero.
Back to ibm_mainframe-Ifmib MIB page.
IPHost Network monitor allows you to monitor ifSpeed on IBM device via the SNMP protocol. Download IPHost Network Monitor (500 monitors for 30 days, 50 monitors free forever) to start monitoring IBM switches right now.