Hi John,
as long as you keep the SOI Manager and MQ Server process on the same machine (which an upgrade to SOI 4.2 does), you can continue to use Catalyst 3.4.1 without any problem.
For the Catalyst-based version of the SNMP Connector you even have to use that version, because this connector is not compatible with Catalyst 3.4.2.
MichaelBoehm