I took a bunch of pictures showing the various combinations of Bosch and Festool chucks. A lot of the pictures illustrate that the bit will simply not be able to drive the screw in so I've only attached the images that actually show a viable means of screwing a corner bracket into a corner.
I'd say that the Bosch Flexiclick Offset chuck works most effectively, well because this is seemingly exactly the situation that it was designed for.

The Festool right angle chuck works almost equally well with or without the addition of the Centrotec chuck - although the green Centrotec chuck release did rub against the wood leaving a slight mark.


You'd probably be best served using a longer bit or bit holder with either the Bosch Offset or Festool right angle chucks (without the Centrotec chuck) otherwise you need to angle the bit a little which as we all know tends to cause cam out.



I did note a couple of things:
I still prefer the way the CXS feels in my hand compared to the Bosch.
The belt hook seems very handy, although I have yet to actually try hooking it to myself.
The magnetic chuck on the CXS was a really nice feature - none of the Bosch chucks are magnetized so the screw kept falling off when I was setting up the pictures (annoying just like what happens in real life). I was using Bosch impact bits, which are are not magnetized so I suppose I could have used some other bits that were magnetized or use a magnetized bit holder.
I was also drilling some 1 1/8" Bosch Daredevil Spade bit holes through some 2x4's. The CXS didn't have the power to drill a single hole. The Bosch was able to drill the 4 holes that I needed, mostly without problem. In most cases you'd use a more powerful drill when using a spade bit, but I thought I'd just mention again that the Bosch is in fact more powerful.
I hope this was helpful. Please let me know if you wanted me to take pictures of anything other type of comparison.