Before C2D, the Opteron series (namely 165) was popular amongst the overclocking community for all applications including gaming. Monster overclocks have been obtained by some people (particuarly with water cooling) which gives great results in any application (gaming, video editing etc).
The Opty series also have more cache than the earlier 'standard' (eg X2) dual core Athlon's which lends itself to better performance at the same clock speed. AFAIK aside from more stringent testing there is little more difference between the architectures of the two chip product lines.
If you already have a watercooling setup and a 939 motherboard, and you want to get good performance by a large overclock then the Opty 165 would be a good choice.
If, however, you want a great games machine and are looking to get a Motherboard/CPU combo then its DEFINITELY Conroe FTW. I'd recommend an E6600 w/ comparable motherboard. It has more cache than the E6400 and below (outpacing the lesser CPU's by a fair margin), offers very good value for money and can be easily overclocked to E6700 speeds and much further. The E6700 / X6800 are more expensive and yet don't offer performance gains to warrant the pricetag over the E6600 in my opinion.
Also, Intel CPU's have classically performed very well in video editing applications (e.g compressing a video in DivX). The Conroe is no exception - demolishing even the heaviest overclocked Athlon CPU's in both gaming and Video Editing.
For me, it would be an easy choice. Plus, the Core 2 Duo will run cooler and consume less power than any AMD CPU, particularly the FX series, and even an Opteron. As you overclock, this difference would widen significantly.