It is best to look at the brightness in lumens rather than the power consumption when comparing lamps. Incidentally, halogen lamps are often quoted as using 70% of the power of old fashioned bulbs, so are not much more efficient even if labelled 'eco'.
It's worth buying one or two lamps for testing, or borrowing them from another boater for test purposes. One thing to watch out for is radio interference, since it is not uncommon with LED lighting especially when the radio signal is weak.
To find suitable replacements for the styles of bulb used on boats, you might need to look at a specialist supplier, for example: http://www.bedazzled.uk.com/12v_LED_Bulb_Replacement.htm