I have all of them from 2x2x2 through 9x9x9. Last I checked, Amazon had 10x10x10 and 11x11x11. Unfortunately, both were way too expensive for something I was going to solve once just to be able to say I did it.
My favorite is the 7x7x7. It’s the last one to introduce new pieces. Solving the 8x8x8 and the 9x9x9 didn’t require me to introduce any new moves, they just took longer due to the number of cubes to move.
5.25 seconds, as of a week ago, which is probably what prompted interest in the topic.
(and the last time AI checked, it was 3.253 seconds)
Yes. The bigger the cube, the more tedious the solve… But not exactly harder.
The even order cubes, (4x4x4, 6x6x6, etc.) do have parity errors, which requires a different algorithm to get out of. But solve a 3x3x3, and you have the basic skills to solve all higher order odd puzzles, and the even ones too if you don’t get a parity error.
Phenomenal. (The 5.25, I mean… The 3.253 is awesome, but it IS a machine after all…)
I forgot to mention, anyone interested should really do some searching on the web to see what has been created/invented since the 1980’s.
Not only the higher order cubes, but the cuboids, (3x4x5, for example), which allow shape shifting, jumbling and a bunch of other stuff.
It can get a bit over the top. But there are some serious puzzles out there for the serious puzzle-minded.
There is a guy in Vietnam that makes custom cubes for folks, and from what I have seen and read, his quality is superb. Can’t recall his name, but it’s easy to find.
I’ll post a link when I find it.
Even the odd cubes larger than 3x3 can have parity issues. Think of it this way: If you take a 5x5 cube and decide not to care about the middle “cross” on each face, you’re effectively solving a 4x4 cube.
Well, yes and no.
In practical terms, there is no parity on a 5x5x5. On a six-colored cube, once you solve a side, it’s solved. If you have a picture cube, where every cubie needs to be in the exact spot it started in, then yes, you can have parity.
I’ve tried posting a youtube link to the most amazingly difficult puzzle I have ever come across. However, every time I try to insert a link, my browser crashes.
So, go to youtube and search 7x7x7 ghost cube.
The user is SuperAntonioVivaldi. He solves the thing in 8 seperate videos. Each about an hour long (give or take.). And no, I didn’t watch the whole thing. 
I don’t know how he stays married. :D. No way would I ever had the time, skill or desire to solve this thing. And my wife would have tossed me out on my ass.
I do own a 3x3x3 ghost cube, and it is a bear.
I’m being really lazy here. But what makes it a "ghost"cube?
My 12 year old neighbor can solve a cube in about 15 seconds and has been obsessively been trying to get this time down so he can compete more effectively I think his record is 9 seconds. Not bad for only working on it for a year or so. He also has a variety of cubes he has saved up to buy, including that 17x17x17 monstrosity. He has echoed others here that it is no harder than the 3x3x3, it just takes longer.
Anyway, the real reason I am commenting is to add to and support Martian Bigfoot’s posts above about seeing the cube differently. I have surreptitiously rotated a corner piece or edge piece to mess with my neighbor and he recognizes it immediately. Both times, he took the cube, looked at the different faces in preparation of solving it, and saw exactly what was wrong with it in about 5 seconds. Really shocked me.
To follow up on this…
When I started back into the Cube as an adult, trying to solve it, and then, when I did, to speed solve it, I realized I wasn’t going to get much faster than 80-90 seconds.
So, I did some youtube searches and watched some of the tournaments.
Many of the kids are turning so fast their cubes will explode (I think they call it “popping”) and pieces fly everywhere.
One kid (and I think it was Feliks Zemdigs, but could be wrong) was speed solving a 7x7 and was nearing completion when his cube came apart. For me, I’d have been done… Not him. He went around, picked up all of his pieces and knew exactly where each piece needed to go (pre-explosion) and then completed the solve.
I can’t see the cube like that. I wouldn’t have been able to find the pieces and put the cube together in a completed state as fast as he put it back together in a semi-solved state. He was able to put the cube in the state it was in when it popped, and had a few moves left to finish the solve.
I don’t know how to train my brain to do that, nor do I know if it is even possible for me. I certainly don’t think you can teach it. And I think it is no accident that kids do it, because their minds aren’t as “cluttered” as adults, they have a lot of free time to experiment and practice, and their fingers are smaller and more flexible. I have never seen a 20-something person winning a tourney, although there are young 20 somethings that can solve the cube in 20-30 seconds. But to get to 10 is such a leap, and takes more time than most people have to dedicate to it.
Either that, or these kids have minds that can see a cube differently from the moment they pick it up.
I’ve seen my nephew operate a playstation control, though, and that fascinates me too.