Basically you're right with the two options:
either you drive it (1) at low voltage and high current or (2) at high voltage and low current. (1) has two disadvantages: the high current causes lots of ohmic losses in diodes and cables, additionally you are running the diodes in parallel which means that if they are not perfectly matched they will run at different currents which can or cannot lead to problems... I guess they are pretty well matched as for other parallel-chip LEDs (P7...). Option (2) is my favorite since you work at much lower currents and thus probably arrive with a more energy-efficient DC/DC converter. The drawback is you have to make a much more decent constant current driver which, depending on the battery voltage, should be able to buck/boost to the correct high voltage... some built-in overvoltage shutdown / short circuit would also be nice. Take a look at my last project
for some details of a DC/DC converter running at 8V-13V and driving up to 27W (Osram Ostar). It is quite flexible and has a programmable output current (microprocessor controlled) and output voltage pretty much anywhere between 2V and ~40V.
The description is not yet complete (details of the firmware and other stuff) but might be interesting for you. Feel free to ask questions if you have some.