After u oven the card, does it has any performance drop on the Graphic card?

U need more heat, especially with modern ROHS standard, manufacture are required to use lead-free solder which melt at roughly 217C, compare to the leaded solder which melt at 180C. A hair dryer only can provide at best 110C. Try a heatgun next time.

And also there another myth that circulating around
Some say that it is not the BGA solder itself that gone bad, is the bumpgate itself that is bad, bumpgate is the joints that connect the silicon die to the chip carrier. In the layer, the solder is ruined. That also can be reflow to get it fix temporally, and that also what explain why some laptop after a reball the exact same prob come back again. During the process of removing the chip from the board, the bumpgate are exposed to heat therefore being "fixed". Is the process that fix it, not the reball that fix it.

Specifically for apple, i dunno where, but most of the laptop specialist repair shop got do. And don't ask me where to do, because i never send my stuff to get it done before.
Before u think of reballing, watch this :

Hmm... So in the end do u resolder those cap back yourself ?

And also another advise is don't attempt to bake cards that still using electrolytic capacitors, they are rated 105C max, u are gonna heard it burst and pop.