Matter of preference indeed, but with Spellbreaker you don't need fortify health as you don't take any damage with it raised.
You still take damage with it raised. The block damage reduction is 85%, so you still take 15% damage. That damage can be a little, or it can be lot, depending on who you are facing.
Magic resist, 80% is the max I think, so it still lets through more than Spellbreaker as well thanks to Spellbreakers straight 50 magic damage deflection then you can take off whatever is left with magic resist effect on other items of clothing etc. Just take a look on UESP wiki how few staffs or spells can actually get past the 50 alone, before factoring in magic resist afterwards.
I think you are looking at player spells, not enemy npc spells. Enemy spell damage can easily do over 400 damage on Master. Fight Malkoran at any level and difficulty and let his Ice Storm hit you, you'll see he does way over 40 damage (Player Ice Storm damage). Also, you must lower your sheild to do damage correct? Often I find myself facing more than one caster at once, that's where magic res kicks in. If you can kill high level mages by keeping them in front of you and never lowering your shield to do damage and never having spellbreaker's ward break on you...then good on you. I play on Master and that has yet to ever happen to me. I must drop my shield to attack and when I do I eat an enemy spell, mages also do over 150 damage every single time at lvl 35.
Matter of preference indeed
Indeed.