と来たら・に至っては: the difference
と来たらN1
Meaning
For …
Past papers
Example
夏ときたらやっぱりキンキンに冷えたビールですよ！
When it comes to summer, as expected, a cold beer is the best!
に至ってはN1
Meaning
When it comes to, As for, In particular, What is worse or more
Past papers
Tested once in past papers
Example
父親はパソコンならともかくスマートフォンに至ってはまるでお手上げらしい。
My father isn't too bad if it is a PC, but when it comes to smartphones he seems to have given up.
How to tell them apart
「〜と来たら」: spoken and emotional; either enthusiastic praise or exasperated complaint.
「〜といえば」: a plain association, 'speaking of A, B comes to mind'; calm in tone.
「〜に至っては」: formal; picks out the most extreme, worst case for harsh criticism.