Heat pumps are 2 to 4 times more efficient, and if you are in MA you can get upto a $10,000 rebate and 0% loan when purchasing a heatpump. Why would you stick with oil heat? Even if it drops to $2 it will be much cheaper to have a heatpump.
I got quotes for mitsubishi systems ranging from 31k to 39K. Ended up going with an LG Red system for 19k. I then installed an heat pump water heat myself so am now fully off of heating oil and it is great.
Also the rebate depends on also insulating your house.. which is a good idea in all cases, but not cheap either.
Whereas replacing the furnace and AC was a $9k job and there were some rebates for that, too. Electric bill is already down, and gas should be down a bit.