Single speed dirt jump specific frame for general riding I am in the market for a new bike and come from a background of mainly cross country (XC) / all mountain (AM) type riding but have ridden BMX also in the past. I'm not averse to standing up and only having one gear, being quite an aggressive rider I am quite open to the idea of 'less to go wrong the better'.

The area where I live offers varied terrain including; canal paths, nature reserves, dedicated blue route mtb trails and a bmx track. My last ride was a full suspension AM specific build but it was overkill for the area and I am looking at getting into more street/dirt jump/pump track related riding but still ride the occasional XC / AM ride (2 - 3 hours) to mix things up.

My question is; 

Would a single speed dirt jump specific frame offer me the flexibility to cover XC / AM occasionally but still allow me to ride from A to B and do some park / dirt riding, or would I be better suited at looking at a 'hardcore hardtail'?
My short answer is no.  A true dirt jump frame is going to be horrible for short XC riding and even worse for extended 2 to 3 hour rides.  You won't be able to get the extension to pedal efficiently and will just end up wearing yourself out standing.  I have a dirt jump frame and after only a couple short commutes on it (4 miles) I decided it wasn't worth commuting on it.  A "hardcore hardtail" looks to be closer to what you should probably look at.  It should be far more comfortable for extended riding, but still handle the abuse of a dirt track.