OK, having a little more success now, one of the reasons it seemed so slow was that 'full tracking' is set as a default, switching to 'fast tracking' speeds things up a bit. 

Now I have the render option set to two threads using a separate process and things seem much quicker. The roadster is clearly a highly detailed item though. Loading a saved scene with simply the roadster takes 130 seconds, and this image took 10 minutes to render, with both my Athlon FX60 cores being fully utilised (at 100%) on final settings in firefly.