I based my opinion on reviews like:
http://www.tomshardware.com/2005/11/21/the_mother_of_all_cpu_charts_2005/
which is maybe not completely fair.
Note, they do not specifically talk about the 805, so maybe the 805 is also an exception from the 800 series in general. Also, overclocking is a gamble, so if you are unlucky, you might not get any extra speed from your CPU and you will not be able to return it for that. I would personally not consider overclocking potention a deciding factor when buying a CPU. I prefer my PC not to crash in the middle of a game etc. or spend R1000 on extra cooling after saving R500 on the CPU itself.