It wasn't particularly photogenic but here is a diagram;
Following this i tried extending the chimney, roughly doubling the height with another tube and connecting tube. Temps didn't fall much at 2GHZ (already fairly low for stack effect), maybe a 5*C fall IIRC. However, perhaps more interestingly..
2.8ghz / 0.975v
GPU 1GHZ / 1.3V
QPI 44x175 / 1.21v
RAM 1750mhz / 1.64v
80/1*C prime 95 peak (in-place large FFTs)
Here the airflow was much more noticable... perhaps like an undervolted 60-80mm fan at the exit of the chimney.
Onwards and upwards to greater things and some overclocking
CPU @ 3GHz/1v, GPU at 1050 /1.4v
After around 15mins of priming on an already hot HS, i got bored of priming; it was at 81*C and nearing the end of its temperature curve. Playing GTA IV gave a stable, max temp of 70*C. This is a good indicator as nothing real-world i have done yet has delivered temps like p95.