Pretty nice. Having read the thread and replies my advice is this:

1) Have Flaming Ace add extra fire damage to the at-will equal to your Int/Con/Cha modifier.

2) Change the wording of +1 dice on Overchannel to +1d8. It's cleaner and less ambiguous.

3) Increase the base damage of Sun Scorch to 2d6.

4) Keep Contagious Immolation as is. It's awesome.

5) You might want to lose the attack bonuses on Flaming Crescendo. Alternatively, reverse the bonuses so that the primary attack has a +3 to hit, and so on.