This is a situation where the physical disk configuration may make a real difference. If the journal and the data files are on the same disk, a write-heavy load will be continually seeking between them. If they're on different disks, there's a lot less seeking, and that may reduce the performance penalty quite a bit (at the cost of extra hardware).

And of course, if you're on SSDs, this is all a non-issue, but that also still comes at a premium.