Those numbers aren't accurate anymore. Red Sea changed there values, and instant ocean doesn't get 1350 mag.. it's more like 1250.
This is what RS "should" mix to now
As far as a previous post about RC having a bad rep. Years ago they had some bad batches of RC, and they changed the formula around a fair bit. IO seems to be more in line with what most people want (well even 11dkh is high in my books 9-10 is what I'm looking for).
The best salt I've found is hW, but for the amount of water changes I do I found it was getting a bit pricey, however it's not to bad compared to D+D, or Tunze cost wise.
IO seems to just work for me and you can find it for less then 40$ for 200 gallons. The only downside is having to buffer you mag (cause it's not giving me 1350!), and I can't do to large of a water change or my alk jumps. The other day I tried to change 30 gallons on my system and saw a .8dkh a jump which is to much for my liking so I need to just stick to smaller water changes until I add the new frag tank on and double my water volume.