Interesting thing here is that your low back is slightly rounded even before you start to lift the weight off the ground. This hasn't, obviously, resulted in a problem for you during all this time seeing as you've made it to 390 lbs. for five without (I'm assuming) having experienced an injury. At this point, I'm not sure how imperative it is that you try and fix this little idiosyncrasy.
You're right, these looked strong, and you appear to have quite a bit of progress left in you. Nice work.
-Stacey