What's better: dual-channel memory mode or a bit more RAM?

[Adam Funk]

On 2011-04-27, compdoc wrote:

>> Will A or B give me better performance?
>
>
> One thing to try is memtest86+. Test both A and B configurations, and memtest 
> will tell you how fast the bandwidth to the ram is. You probably won't see a 
> lot of difference.
>
> I've been reading that with quad cores, you want to run in unganged mode. 
> (which turns off dual-channel mode) This allows the cpus to access the banks 
> of ram independently. This is supposed to be faster.

I'll try the memtest86+.  How long does it take --- roughly, so I can
plan it in --- minutes, hours, all day?