Im wondering what PSU you will use also... IF u plan to SLI GTX780 you need at least a 850W good PSU for that machine.
Msi Gaming GTX 780 OC , Gigabyte GTX 780 OC, Evga 780 ACX SC, Palit Super Jetstream at the moment seem the logic decision, since they get pretty much the same FPS as a Titan for 300$/350$ less. Palit will use 3 slots, thats out for me. Gigabyte is 11.4" long... I have come to the decision of MSI 780 Gaming or Evga 780 ACX SC. Yes, im also buying to upgrade my GTX560 SLI.
MSI Gtx 780 Lightning might have or might provide more juice (with custom OC) sure, but I doubt you will see practical FPS gains coming from either MSI gaming or Evga w/ ACX SC, since you can also OC each of this a little bit more.