gonna switch to cab grow eventually, lighting?

I've got a 400 watt HPS for a 4 spot hydro system right now and is doing the job quite nicely. However, I wanna switch over to a small single lowryder cabinet system in a few months. Would it be best to just install the 400 watt in this and cool tube it, or would it be better to just do a 100 watt light? The money for electricity isn't an issue as power is pretty cheap in my area. But, 400 watts for one plant seems like quite a bit. Opinions?

why lowryder? if you got the 400hps just hook it up with a cool tube as you said and set up a scrog cab and grow a "real" strain. not that lowryder isn't real but there are so many better choices, i just don't see the attraction to lowryder. yeah you can go from seed to harvest in no time but the quality just isn't there imo.