Mine was a head converted into the 1x10 red fang combo. I used the cab a little before I put the head in and it really sounds about the same as an ext cab as it does a combo.
I'd reccomend getting the Z conversion cab and the red fang is worth the money. Then you have the option of going either way.
I kind of look at mine as a super mini-z now because all you have do do to still use it as a head is unplug the internal speaker and plug in a cab (with it turned off of course). It still looks great sitting on top of my 1x12 Z cab, and when I need to be heard better I use the bigger cab. I just got the 1x10 in the same color as what I already had. The convert was pretty easy. I solder so I added a swithcraft 90 degree plug on the speaker so it would be a true combo. The directions for the cab explain this to you. It is not hard to get it all set up in a couple hours.
I would imagine that the combo and head + 1X10 cab would sound the exact same as it would be the same cab either way. It would be cheaper to get the 1x10 combo but if you got the head and 1x10 cab you could convert the cab to a combo, it would just cost you more money.
"Bold simplicity is the keynote to good design.” Nov 20, 1970 Norman "Sailor Jerry" Collins