If the "90" is $9.5K and the "80" is $10K and you'd pay $1200 a season to cool with the 14 SEER you'd pay $1120 a season for the 15 SEER.I've narrowed my choice between 2 companies, one wants to put in a Trane 90 plus furnace with a 14 seer ac unit but I would have to repair holes they need to make to run some piping outside. Another wants to put in a Carrier Infinity 80 percent variable speed with a 15 Seer Infinity ac unit and Infinity controls. There is not much of a difference in price.
The money you sink into either system with these numbers becomes equal at ($10000-$9500)/($1200-1120) = ~6 years. If you plan to stay in your house less than 6 years you should go with the 14 SEER.