HO - High Output
XHO- Extra High Output
40 - E40 socket

both HO and XHO us an E39 socket.
I don't know the exact differences between those bulbs this is the first time I'm seeing them, but that should help you identify which bulb you have.

You should look at a spectrum chart for your current CFLs as well and compare to the MH. Plants use all colors but mostly blue and red. Check out this chart Berowra Waters Algal Bloom Monitoring its a random webpage but it shows a chlorophyll a and chlorophyll b response. This chart, following the importance of chlorphyll activity of c.a. and c.b. and disregarding other factors like carotene, is seen that the best wavelengths of light ... are found at ~420nm 460nm 630nm and 660nm. That should help you identify which wavelengths are the most important when choosing a bulb.

I say get the HPS. Both MH and HPS can sustain a plant throughout it's entire lifetime, but the HPS has been proven to be better at that one thing we all grow to begin with and that's buds (or fun and what-have-you)