Hi Farooq:
SAP reommended (the maximum allowed i have can't find it).
messaging.syncMessageRemover.checkInterval 5 minutes
messaging.syncMessageRemover.messageCount 1000
These values are mentioned here: http://help.sap.com/saphelp_nw73ehp1/helpdata/en/48/cbb487cea80783e10000000a42189d/content.htm
xiadapter.inbound.persistDuration.default 86400000 ms (1 day)
xiadapter.outbound.persistDuration.default 86400000 ms (1 day)
These values are mentioned here: http://help.sap.com/saphelp_nw73/helpdata/en/48/c8563ff63335bfe10000000a42189d/content.htm
To increase these value could provide memory leaks or db problems. To increase them depends about your Hardware and i think it will be difficult to find any general recommendation.
Regards.