OK I am gonna try to tackle the math. This assumes that my opponents have 30 MR since that seems to be the most common number at the start.
The constants are MP reds as well as 10% MP from the offensive mastery tree. oh and dominion gives 5% MP from the crystal scar aura. The MP reds give 8.55 MP, while %s stack multiplicatively so I believe that 5% and 10% would result in 14.5% MP.
30 MR gives 23% damage reduction, it think. If that is correct:
Taking into account MP reds, masteries and the aura, you get 30 - 8.55 = 21.45 x (1 - .145) = 18.34 MR which is 15.5% damage reduction. So, I guess this would be the baseline.
Also, at level 3 my spells do 89, 97 and 78. The ratios are .65, .60, and .55 respectively.
Soooo, if I just added 20 SP boots (scenario 1), I would take 30 - 8.55 - 20 = 1.45 * (1 - .145) = 1.24% dmg reduction or pretty close to true damage. My spells would do 88, 96, and 77.
Scenario 2 is buying Boots of Speed and a Blasting Wand (40 AP). My opponents magic resist would be the baseline ie., 15.5%. However, my spells now do 115, 121, and 100. Applying the 15.5% magic resist, the numbers are 97, 102, and 84.5.
So it would seem from a straight up damage comparison, scenario 2 does more dmg/spell. Again, I understand that faster boots can help do dmg, health helps keep you alive, CDR, etc.but that isn't the point.
Let me know if I don't understand the way these things work. Thanks.