People should start trying to figure out exactly how Flametongue is scaling. On the beta it seemed to be getting normal spellpower scaling and then something like an additional 2-4% coefficient off attack power. Also need to confirm whether or not it's scaling correctly with mastery now.
I did a couple of preliminary tests and so far it would seem that you are correct about the way Flametongue is working. In my tests it appears that Flametongue is in fact scaling properly with Mastery, and it seems to gain another ~4% of my attack power. Also, the attack power scaling seems to only occur if you are spec'd as Enhancement, which isn't a surprise, but I thought it was worth mentioning.
The attack power bonus doesn't seem to be linear, but that might just be a problem with my formula. I just tacked on the bonus to the end, but it seems like attack power is providing a larger bonus the more of it you have. I'll try and work on this some more in the next few days.
Test 1: 5216 ATP, 3041 SP, 15.97 Mastery, 2.5 Weapon Speed, Enhancement Predicted: ((274 + (3041 * 0.15244)) * 2.5/4) * (1+15.97*0.025) + (5216 * 0.04) = 853.66 Tested: 859-860
Test 2: 432 ATP, 629 SP, 8 Mastery, 2.5 Weapon Speed, Enhancement Predicted: ((274 + (629 * 0.15244)) * 2.5/4) * (1+8*0.025) + (432 * 0.04) = 294.69 Tested: 293-294
Test 3: 4542 ATP, 349 SP, 0 Mastery, 2.5 Weapon Speed, No Spec Predicted with ATP Bonus: ((274 + (349 * 0.15244)) * 2.5/4) * (1+0*0.025) + (4542 * 0.04) = 386.18 Predicted without ATP Bonus: ((274 + (349 * 0.15244)) * 2.5/4) * (1+0*0.025) = 204.5 Tested: 204-205