Do not ever overcook either of them... 10 minutes max per inch of thickness whether grilled or baked. Cod will be very flakey and moist if not over done. Both are difficult to grill without a basket or plank.
A piece of slate flooring tile makes a very good plank for cooking on in the grill.
I just cooked cod several times last week and just panfried it in butter after a roll in lightly-seasoned flour.
AMA just came out last year and admitted there was absolutely NO science behind their long time claims for low-fat diets. It was purely a marketing device for dairy.
The 8-10 minute thing is from the Canadian school of fish cooking and is near perfect for getting it right...
I start grilling halibut skin side up for 3 - 4 minutes, flip and when the skin starts to stick to grill the filet will easily lift off and will be cooked to perfection. (another 4 -5 minutes depending on thickness)
