8x is always fine for me. I've also had burning pause as the buffer runs low as I've been running a load of other stuff, caused no problems at all. I also use Verbatim.
I'm no expert, but I read somewhere that real low speed burning can do more harm than good... but then, i've never had any need to experiment as never had a single disc read error.
Mastertards advice sounds about right to me.
Also, no patching or anything required if you're burning iso's from the same region as your wii, but i also check mine with regionfrii to make sure I've not got something thats not quite what it says it is.