Can you explain how you get the number 31.5% damage and what you mean by "after haste modification?"Uh...I knew I would soon speak something noobish in front of you, Mr. Stasik. I'm so utterly embarrassed now. Still, it's better to know late than not to know, and now I won't have as much pressure to refresh my bombs.
I did some very quick mental calculation just now, though. I believe bombs also benefit from Mana Adept. A extra tick of LB is a little more than 9450 haste, and adds 25% of base (0 haste) damage. The same amount of Mastery would give me 31.5% of total (after haste modification) damage. Is this argument plausible? If it is, does it indicate to enhance bomb damage, an arcane mage should stack mastery in place of haste?
I tend to speak specifically for frost, however DoTs function the same for any spec. DPET gains at breakpoints are rather significant though. I actually did a hypothetical analysis based off 5.4.7 stats (so it would be ~item level 580) which takes into consideration stat tradeoffs. DPET gain by moving from 9577 to 18974 with Living Bomb is 14.28%, whereas the jump to 28k was determined to be 12.50% because of the amount of stats one must sacrifice (crit/int) to get to 28k. Here is a chart which represents stat combinations:
You can see that amplification does play a role, and now that we can reach item level 588, I should update this chart to go one more to the right with updated stat combinations (my argument is that it is worth it to go to 28k haste if you do not have to break socket bonuses):
As I try to think of how you came up with 31.5% from mastery gains I also look at some analysis I did about changing mastery levels. For arcane everything is increased by Mana Adept, however the gap between LB ticks is very large and would require giving up too much mastery to go for 18974+frost armor or whatever its equivalent is with mage armor (~23k?). On multidot fights like TFP and Galakras, Arcane can benefit from Nether Tempest breakpoints.
Frost is limited in its benefit from mastery as it only scales with icicle generators. This is a good thing, otherwise frost would only care about mastery. DPET gains from mastery are only on Frostfire Bolt & Frostbolt, and they have a difference of 14-16% depending on your gear (i.e. if you stack mastery those spells will do ~15% more dmg than if you stack haste or crit).
More info on how I analyze those stats can be found here.