This is going to be a long response so hold on.
Lets see, first a few corrections to your list.
An NV4500 isn't a t-case, it is a heavy duty 5 speed transmission that somtimes has a granny low, very strong unit granted the 5th gear issue is resolved
A Dana300 isn't nearly as strong as you have listed in stock form (maybe this is assumed beacause upgrades are added into your price?), and once you put big outputs and gears in it you have quite a pretty penny invested. Some people have broken the cases on the dana300 just like I have done to the cruiser case, some people say that happens becasue the case wasn't properley supported.
Some people have also broken the after market gearsets for the dana 300 also, there are several companys that make these gear sets and i think only one was failing but i'm not sure which so I won't name names.
The orion is a very strong unit with exception to the stock nose cone if you get the standard orion, The HD version provides a new nosecone that should resolve all issues.
I don't think there is such thing as an AtlasI anymore unless you buy used all AA sells are AtlasII's
As far as locking the fj40 case in place this would induce more stress into the case from frame flex and motor torq. Marlin makes the best t-case saver I have seen but i don't think it would have prevented my last failure.
There are lots of reasons i'm going the atlas route, lots of those reasons I listed above but I'll cover them in more depth. The short of it is, that it is going to be the last t-case I ever have to buy no matter what rig I have. The long of it is:
-Adaptablity, the atlas is based on a D300 and can be bolted onto just about any transmission you can dream of and lots of doublers are options as well. For the short term mine is going behind my sm420, long term i'm going to swap in a 2uzfe with the A340(?) tranny this adapter is only 3/8" long and should work out very well.
-Gear selection, you have a choice of a unit w/ ratios: 2, 3, 3.8, 4.3, 5, and 6. I'm going w/ a 5.0 unit for my future stage, my good freind has a 2uzfe in his truck and when he is in his 4.7 ratio it kicks ass at GITTIN IT, he has lower choices also which is nice. Lots freinds have 4.3 units and they don't seem to be enough gear for around these parts coupled with an auto, they have to rely on horse power and they don't seem to just crawl.
-Clockable, The bolt pattern on the front is round and you can run it at 4 different positions at about a 25deg range, getting a flat belly should be easy. big deal to me
-Front dig, this is also a big deal to me, not many other units have this ablity, d300 does and I think an np205 can as well but don't quote me. Front dig adds a lot of mauverabilty to your rig.
-Strength, Quite simply it is very strong, I am not worried about it ever failing. I have 10 wheeler friends that have atlas's and they all wheel the s*** out of their rigs I only know of one failure ever to of occured which leads to the next point
-Warrenty, AA stands behind their product, my friend had a sycro that failed and destroyed his case, this was a freak accident. Mark was not the original owner of his case and even though AA clearly stats that there warrenty only covers the original owner, they fixed his case at no charge. That is a stand up business
-Shift on the fly, you can shift it when you are moving, cool and practical
-Price, all things concidered, atlas's are not gold plated, they really are not that expensive. People don't seem to blink twice at invest 2G in there front axle or their motor, why not the heart of the drivetrain?
-Compact, It is simply smaller than other options. In an fj40, even with my wheelbase stretched a foot there isn't that much room.
-Custom builds, AA is getting toyota bolt pattern flanges from high angle drive line for me and building my case with them so I can continue uses toyota d-lines and not require me to install the flanges on my own
Things that turned me off on the other options
-Stak, I almost went this route the reasons I didn't: heavier, not sycro'd, price increased making it in the same range as atlas, last i knew they were 3 months out, gear options are 3.75, 4.33 and 5.44 I wanted 5.0 (deal breaker)
-Orion, good affordable unit that is direct swap into my current setup but I don't want to be stuck with an ofset rear axle and no front dig, I don't think it can go behind my future plan witout a toybox
-dual mini cases, every one of my friends with dual mini cases has broken output shafts in either the front or/and rear case. Too long, Not that cheep, no front dig
-Toybox/Splitcase, thought long and hard about this seams like a very good stout option, once again ofset rear, no front dig, long, not that cheep
-d300, needs a lot invested to make it what I want and still may not hold up, I don't want t-case problems anymore.
-Lomax, never really considered it but seems like a good option, might be a bit large and def heavy
Sorry for the epic response, I was in your shoes a month ago and have a lot of thoughts on the subject. Also sorry about my spelling I don't have a word processor on the home machine.
Just my .02
