Yes it is possible to underclock the 614c, I do, and can get 3+ days out of it with light use.
If you still have your iPAQ Choice points then there is software you can purchase there called Pocket Hack Master:
Pocket Hack Master @ iPAQ Choice
There is also another program called XCPU Scalar 2007 which can perform the similar tasks:
XCPU Scalar 2007 @ Immiersoft
Both of these allow for customiseable over and under clocking of the CPU speed to boost performance or increase battery life.
Please try to avoid multiple posting in the future...
Current Phone: HP iPAQ 614c - latest HP ROM installed
Current Software: SPB Mobile Shell v2.0, SPB Pocket Plus v4.0.2, SPG GPRS Monitor v2.5.1, Apoxsoft Metrix v2.1.1, Immiersoft XCPUScalar v3.0.3, PHM Registry Editor v0.70, Corecodec Coreplayer Mobile v1.2.1, Opera Mobile 9.5, Picsel Browser 1.0.5, visualGPS CE v1.2, Vito Astronavigator v2.02, smart2go Maps, Tomtom Navigator 6, Google Maps.
Phone History:
Philips Diga, Philips Savvy, Nokia 3310, Panasonic GD67, Motorola MPx200, HTC Alpine (O2 XDA 2i), HP iPAQ 614c