well, i've made a few of these.
the first one i made, i did a runtime test on it, and gave up after 2.5months. the light was extremely dim by that poing, but still lit up. for the first month the light was still very usable.
i sold that one to a friend who wanted it, and made a new one for myself in pewter. this one probably has around 10hours on it.
increased current will decrease the led life...but it should still outlive you /ubbthreads/images/graemlins/grin.gif
basically, after 800ma, a 1watter won't put out any more light, but just get hotter and suck more current.
you'd be better off with the 3d, and taking advantage of the smaller form factor.
if you prefer the 4d, you could add a bit of resistance, but i think 1.2amps would be pointless in terms of increase output, and only decrease ledlife.