There are such sleep modes on FMB devices (not counting gps sleep, not relevant in this case):
1. online sleep mode. GSM is still available in this mode. Device can send/receive sms/data. It is just less power hungry mode than normal.
2. deep sleep. In this mode gsm transceiver is off. Device is not able to send/receive sms/data.
3. ultra deep sleep - improved deep sleep mode. During which most of devices operation is off. And device can wake up only via movement detection via accelerometer.
But basically the above answer is correct. DS mode + max saved records count - would provide what you wanted. Just without that option for manually controlling when device wakes up/goes to sleep.