At this time there is no reason to run with an 64 bit Athlon processor, at least for home use. When the 64 bit version of Windows is available is when I would get ready to purchase a 64 bit processor. Until then it is pretty much a waste of money, especially in terms of gaming performance. Also, the processor's are new and it's not normally good to buy as soon as something is released (as far as hardware is concerned). I usually go by the same rule for Window's when it is released. I give it at about a month before I use a new version of Windows just to see how well it does with the public and what everyone has to say about it.
It depends a lot on money too. Right now 64 bit processor are going to be pretty pricey considering they are new, and especially since 64 bit processor's (for the general public) are a pretty new concept. When it comes to gaming we are finally being able to purchase 64 bit processor's and put them into use, but until the 64 bit version of Windows is available there just is no point really.
So, I suggest waiting until that happens. Until then you might want to look into some high-end AMD or Intel processor. Maybe do some overclocking, buy the right combination of hardware and you will do just fine.