[lightroom speed with OS X El capitan]

Been running El Cap on my laptop for a while now. My photo stuff was 100% unaffected by that. 

 

What sometimes doesn't work for me are built in apps like Mail or Photos. What generally breaks for me are non-conforming apps (unfortunately Capture One was one of them a few times), I never had issues with Lightroom or Photoshop. 

 

I also never had data loss due to this, but I do have a few back up strategies that have worked so far.

[x100s with WCL/TCL and EFX-20 flash]

Even a small hood will block the built-in flash. So, it's a good idea to use a coiled Canon TTL extension cord with the EF-X20. Works okay here, but I rarely use it as it is a pain in the rear to hold the X100T with one hand and the flash in the other. 

 

If it is about ad-hoc on camera flash for snapshots, the Nissin i40 or the Meike 320 are both better options, the Nissin being very expensive unfortunately. If it's a planned setup any speedlight that has manual controls works great. I don't mind going back and forth for adjustments as it slows me down and makes me more considerate.