In an interesting coincidence, I'm going through a similar design exercise with the 5 station ranch project, and I recall a previous thread where we discussed panel tilt angles and such.
I've never cut a design so close as to have to worry about such fine tuning of the voltage dropouts, and you are using WLIP, which limits my other recommendations. I think your choices are as good as any.
Forgive me if this has been answered before, but have you measured the current draw of everything as it was in use so the daily amp-hour need is known?
Are there any power reducing features on the cell modem you have missed? Sometimes there is a setting or jumper that kills the LEDs, which can save considerable power.
Does the WLIP have a programmable upload time, and if so, will the application be OK with a longer time between transmissions? The cellular transmitter is likely the biggest single power drain.
(One of the things we programmed into the WeatherElement data hub is the ability to change the update rate remotely from the server.)
I had some other ideas, but the system design negates them. It does give me some ideas for possible WeatherElement enhancements.
I'm just gonna say empirically, I think you are OK. I measured my solar powered WE station at about 7AH per day. Your site is not that different, although I think maybe the WLIP might draw a little more than my data hub. 60 watts on the panel is an optimistic 5 peak amps. Even just with 2 hours of sun, and 1.1 fudge factor for battery charging, you should be good to charge on a moderately sunny day.
Draining an 85 AH battery to 25% uses about 63 AH. At an estimated 7AH per day, that should run the station for an optimistic 9 days in the dark (negating derating for cold temperatures).
But, only time will tell...
One last thought for next year. Surrounding the panel with some shiny polished metal angled to reflect sunlight onto it would increase its output inexpensively.