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.
I've never used anything less than 16x, I even use 16x with 8x discs. I use a piece of crap BenQ generic drive that cost about 50 dollars 3 years ago. I recently bought a spindle of 100 store brand 16x DVD-Rs for 22 dollars and they burn magnificiently.
I think it's ridiculous to even suggest that you should burn at anything but the default, highest speed setting when you don't know what drive he has.