Thank you, that's what I was afraid of. It seems the upgrade to 15" retina is not worth it and I should stick with a 13" Air then.
1. If you're offsite far more than you're onsite.
2. If you need >8 GiB of RAM.
Of course, if you expect to do much gaming on your laptop, you may want a laptop with a dGPU. *8-)
Agreed on the gaming part. But one wouldn't buy a Mac to play games lol.