Sorry, been off ordering school books for this semester for the last 3 hours or I would of posted back sooner.
Anyways, I actually don't know what "lake tiny" is. Haven't heard of it before, but if its power saving for SSD I wouldn't even pay attention to it. I mean, I guess more power savings is good, but SSDs use ridiculously little power. The motherboard in a system usually only uses around 6 watts of power, and you would need at least 5 SSDs to even tie with that if they use a lot of power. If they are energy conservative you could well need 20 to equal the power usage of a motherboard. So this idea of an SSD power saving feature sounds extremely minor.
The only real advantage a "Z" chipset has is overclocking. Unless you plan to overclock, I would just go with a different system. Though I have seen some Intel CPUs undervolt really well, like my old i3-3225 which can run at -.50v. you might want a "Z" chipset for that.
If your ultimate goal is low power usage you might want to consider going with either an Ivy Bridge system, or a cheap Haswell CPU and upgrade when the next Intel CPUs come out. Ivy Bridge uses less power than Haswell, but what comes after Haswell should use much less than either.
As for occasional gaming, I wouldn't be too surprised if that Pentium was giving you some bottleneck. The 7790 is a pretty good card and while you won't max every game, you should play at 1080p with average settings easily. You might consider overclocking it a little though, since AMD usually overclocks really easily, and really well. Took 10 minutes to overclock my 7850's.
I personally wouldn't advise crossfire anymore to people. I have two 7850's in my PC right now and I have been really disappointed with the results. The main reason I got it was for Total War: Shogun II and it lowered performance. I've seen a little boost in games like Bioshock Infinity, but I didn't really need a boost in Bioshock Infinity. I was maxing it out already, and I would rather use less power and kill the world a little less and get 40-50FPS than get a solid 60FPS. I think if you have been doing that well slowly trading up you should continue.
I know now some have amps for the DAC, but idr it happening before. Then again I missed pretty much everything which came between the end of DDR RAM and the end of 2011 so I probably missed it. Its a bit niche but for some one added feature will win them over.
For that ASrock board, I still would advise against them because their customer support is terrible. If it dies, I would be amazed if they full fill the warranty. The board looks pretty good and well rounded with features, but again if it dies you are out of luck probably. And where they advertise "Digi PWM". They lied about that before, and are probably still lying about it.
For RAM don't worry about the speed, just let it be at 1.5v. Unless you use integrated graphics you will see very very little difference in performance between RAM speeds with good timings.