Well, you have three options: try to pull with a neutral back, switch to sumo, or just keep doing what you are doing and hope that you don't get injured. Some people's backs can tolerate loaded spinal flexion, it's just a higher risk. In my case, I switched to sumo after injuring my back. My technique looked pretty much the same as yours, just slightly rounded, I was pulling over 500 with no problems. One day I was doing some singles with something around 500 and then moved onto down sets with about 425 or so, blew my back out on the first rep. It wasn't really that bad and I was back to normal within a month, but the first week I was in constant pain. I'm able to set up with a straight back but it's almost an SLDL, the logical choice was to switch to sumo.
I have read some of Stuart McGill's work, from what I understand you or anyone who pulls rounded might be better off with lower frequency and volume for the deadlift. You hear of some guys who only pull heavy once a month and that kind of thing, it makes sense because it gives the intervertebral discs time to regenerate. Basically, your discs break down as a result of certain things, particularly loaded spinal flexion, but they also grow back. If you break them down faster than they can regenerate then you are fucked eventually.