reasonable checkpoint interval

What is considered a reasonable informix checkpoint interval? I'm currently investigating a problem on a system with the checkpoint, as shown in /usr/informix/online.log, occuring every 6 minutes or so. This is on a Unix box with Informix 7.12.UC1. Users on PC's have a GUI application to do queries into this Informix Online SQL engine. Every few minutes, their PC's freezeup (all simultaneously) for up to 5 minutes reducing their productivity by orders of magnitude. What checkpoint intervals are considered reasonable? Is there such a thing as having checkpoint intervals too close together? What are the Informix defaults? Users of this system are doing a moderate number of queries typically against extremely large tables all indexed and multiply so. Meanwhile a large number of system batch jobs are running doing lots of table queries. Thanks ahead. --Stuart