Ok, picked up the 690 today and have finished the build, all is running smooth.
So here is a quick comparative review of the 690 vs the 900.
Both look pretty cool, the 690 has a classier feel to it while the 900 has more of a brute force and flash machine to it. The lines on the 690 are very clean and the mesh up the front is very nice as well. Both systems have additional ports on top for easy access (USB,firewire, mic, phones) but if you have your comp under the desk like I do the 690 has its power and reset switches on the right side near the base. Not as easy to access under the desk vs the 900 which has it's buttons on the top. Also, depending on how much you like blue LEDs the 900 has very pronounced LEDs in the front on the two 120 intakes. There is also the window on the 900 if you like looking at the guts while it's running.
i can't really pick a winner when it comes to looks between these two as they are very differnt. If you like flashy and a window the 900 is better, if you like elegant and sleek then the 690 is your case.
The 900 has the best stock cooling I've seen. Dual 120s in front, 120 at the back, 140 at the top, optional 120 on the side. It's a windtunnel. However, the 690 is no slouch either. It only has a single 120 in the front and at the back but there is optional upgrades for dual 120s on the top, dual 120s on the left side, a single 120 on the bottom and an 80 on the right side.
However, IMHO a front to back/top is more effective than a side/front/bottom to top/back wind flow and the 120 on the front of the 690 has a lot of obstructions with the small grate in front and the HDD mount behind it.
Therefore for windflow and air cooling I give this section to the 900.
I tear my cases apart on a frequent basis both to modd them as well as to frequently change hardware setups. The 690 is "toolless" but not really...close in that the HDDs do go in easily but the 5.25s not so much. IMO the design is flimsy and i find the DVD drive is not secure enough with the single clamp on the left side, I ended up adding another screw to the none secured side as i could move the drive when I pushed on the eject button, not much but it annoyed me so in went a screw, quick fix as the case still has the standard holes in place should you want to insert a screw. PCI cards also have tooless securing mechanisms and they seem to work adequately...but its only been a day. The 900 requires a philips screw driver for the 3.25 and 5.25 drives and has thumb screws for the PCI bays.
The 690 also comes with clips along the side of the motherboard to secure cables with. It's not that pretty but if wire management isn't high on your priority list then its better than nothing.. I prefer running cables behind the mobo but that isn't possible with thie 690 without some dremel action. The 900 isnt any better, there is room behind the motherboard but minimal holes to run it to...again ,some dremel action needed.
Both are what I'd call "standard" mid-towers, they don't have a ton of room but enough to install your components, both fit my TRUE as well as my 9800gtx+ with the accelero s1 rev 2 on it.
I've been impressed lately with coolermasters quality for $$$. I find the 690 to be significantly sturdier than the 900. I've taken the front fan bays out of the 900 on a couple of occasions and it's made them difficult to put back in, the clips are worn and don't snap well into place. Also, the front bay covers are held in place with a single screw on each side...unfortunately that means they pivot in place a hair. Thie 690 uses clips on each side which aligns the bay drive covers perfectly, a little cleaner and a more "sturdy" higher quality feel.
The switches on the 690 are a bit unconventional and maybe its just me getting used to them but I'm not a huge fan. I like the old push button switch better. The 900 has a nice little tray on top which fits a pop can or other small items, although I ddin't think i'd be using it much I now always have something in there, SD card, USB stick, paper clips, pen, etc...is a nice touch. Mentioned it once but window is nice on the side, i'm big on wire management and like to show off the work with a window. Unless you don't mind making a window yourself then the 900 has that edge.
and build two systems. That was my solution. If that's not an option then I can't really pick a clean winner between the two.
If you're looking to push your overclocking to the max on as little money as possible without liquid then the 900 is a better bang for your buck. Also, if you like flash, windows and blue LEDs then again, the 900 is a good choice.
If you're looking for good air cooling and a sleeker, cleaner look then the 690 is a nice case as there is no window, the clue LED in the front is not that bright and the mesh with the silver trim is a classy look.
Both are great cases for $$$ in my opinion, its a matter of matching what you want/need to the right case.
Hope that helps.