Zero performance gains according to many sources. You will gain nothing in game and maybe get 10% on load speeds.
I assume you are speaking specifically to PS4's. I hadn't seen any data on it.
For PC's any good benchmarker in summary will note that it depends on the game, and even the level/instance being loaded, but I just posted a slew of videos in the main PC thread demonstrating the objective superiority of full SSD's offer for load time, and for the games where it makes a major difference, it's not 10%, it will sometimes be 400% or faster. In fact, here's a casual post from a user on the Crucial forums I just Googled with some of the steepest differences in terms of seconds for cold/hot loads (HDD load times on the left, SSD load times on the right):
http://forum.crucial.com/t5/Crucial-SSDs/SSD-vs-HDD-game-loading-comparisons/td-p/85884
Batman Arkham City
x x
14 10
Blood Bowl
24 19
34 17
Ceville
15 6
26 4
Dragon Age 2
14 13
9 6
Shogun 2
97 81
29 21
Trine 2
14 9
x x
Witcher 2
14 13
25 10
The thing I think many guys don't think about is that this isn't just about the time it takes to load the game up. It's talking about any time you enter a new virtual space (i.e. "instance") of the game. Every time you load a new level. Every time you pick a new planet on Mass Effect. Every time you die the game is going to hot-load you back to the last checkpoint.
The SSHD's often close the gap, though, so many argue they are a better price/performance purchase than SSD's for pure game drives. I think he hit the optimal performance/value curve with that Firecuda, no doubt. Seems to be the #1 choice replacement drive for PS4's. Still, if you happen to play a game like
GTA V where load times are often huge, and the difference has been vast in certain benchmarks, then these loads start piling up minutes upon minutes on the hour in terms of the additional gaming minutes they offer. It becomes a question of how much you value your time, or the repeated stretching of your patience in each instance, definitely.
I put a 1TB Seagate SSHD shortly after I got the PS4. No problems so far.
Here is a chart for quick comparison of amazon prices.
It's $115 for the 2TB Firecuda for us Yanks at Newegg. It was $99 before the newer version came in. They lifted the price, but I think it will settle back down. That isn't a bad premium at all.