A useful GF100 GPU hack is revealed in Laine & Karras' paper "High-Performance Software Rasterization on GPUs" on page 6.  They state that:

When there are shared memory write conflicts within the warp, the write from a thread on a higher lane, therefore containing a later triangle, will override a write from a thread on a lower lane, containing an earlier triangle. The CUDA programming guide explicitly leaves it undefined which thread will succeed in the write, but at least on GF100 the behavior is consistent and can be exploited.

Good to know!