hqi's are metal halides i believe. And I've read that theres not much of a difference between single ends (SE) and double ends (DE, or otherwise known as HQI) I'm pretty sure they're the same thing, but if not, someone please correct me.
But someone said that de's are better for smaller tanks, and se's are better for bigger ones. I dont really know why that'd make a difference, other than size of bulb, which very well could cause some differences i guess.
btw....what you have on there is PLENTY of light. IMO, theres no need to upgrade at all.