oI'd say going above a coil's recommended wattage may shorten it's life, but I don't believe the wattage you are targeting is necessarily there (sorry don't have it in me to like, check a 1.8 coil stored in the closet, but I think you should be fine.
I have used the 1.6 coil, and that might allow you higher wattage that is still within the targeted "range." It's actually my favorite coil of all three, just enough (a hair) higher wattage and a slightly less restricted "experience."
If you want a warmer vape in that tank, trying the 0.7 coil is not a bad idea. It was a bit much for me, although I found it useful when I was vaping higher VG, and for sure, you could probably go higher on that coil than the other two without compromising coil life as much if you want to go higher wattage. You'll use more battery and more juice, but really, finding the "correct" coil for you may be your best bet to avoid worry. I neither loved nor disliked the coil, but I'd think at higher wattage ranges, you'd get a better vape experience, and coil life. Although I don't think the wattages you are mentioning are a HUGE worry either, except for the possibility of overheating your 1.8 coil and possibly shortening its useful life.
I think all three coils are pretty distinct actually and tend to just be slightly different in terms of vape, draw and etc. If you want to up your wattage, opening airflow some may help keep tank temperatures lower as well.
Best of luck,
Anna