I was going to ask about this. I wondered how much time the game spends loading "levels".
An SSD is a very very good upgrade as whenever you enter a dungeon, battleground, scenario, raid, etc it loads the new zone and the load screen will take time, having said that however, it has no effect on performance when actually "playing", what I mean by that is that if it you go through a portal or teleport to another place it doesn't matter if it takes 3 seconds or 10 seconds to load from a gameplay pov just a convenience pov, your not going to die because of it, and so while it's a great quality of life improvement I would personally prioritize getting my CPU/GPU/RAM performance in line with my res first before looking to pend on an SSD.
WoW loads in new zone data as you cross between them on mounts/foot but on a decent system you won't notice that these days even on a mech HDD, any minor stuttering will be due to the network (crossrealm info surge).
So, it's an SSD, GTX770, Overclocked i5 etc.
As enjoyable putting together a gaming rig is, it's also a bit of a nightmare deciding on how much to spend, and what on.
The spec is kind of running away now isn't it lol, have you considered buying a new Z68/77 board plus a used i5 2500K? that would be an amazing price/performance choice and I generally find CPU's to be the hardest thing to kill in a computer so usually a safe bet for second hand.