Whats the difference between 95% and 96% variable furnace efficency, the cost is $1200 difference

Probably not. You'll have to run the numbers. For example, if your fuel costs $1000 per year, each 1% gain in efficiency will save you about $10. If that extra $1200 is borrowed money (mortgage), the interest alone will cost you more than you'll save. Often the major difference between a 92 and a 95% AFUE furnace is a different heat exchanger design. That last 1% is usually gained through more complex control systems and variable speed motors that will cost a lot more to repair when they fail.