Your math looks spot on to me. 240 armor to gloves is technically better for EHP. A lot of people prefer the 18 stam though because stam can be used in all situations regardless of incoming damage. I consider them roughly even and it comes down to personal preference. If I wasn't an engineer I would have used 240 armor, a lot of people just prefer 18 stam though.
Oh and just a side note, make sure to include warrior (or pally if you're a pally) base health in your equation for how many HPs you have...
I really should put that spreadsheet back up... volunteers on who wants to fix it for me 'cuz I'm lazy! =P
An easier approximation when comparing gear is that 11 armor is ~ 1 stam worth of EHP.
So... 240/11 = 21.8 vs. 18.