Tuning the temperature rise on a gas furnace

Hello. I recently had someone come out to give me a quote on a replacement furnace. He told me that my present furnace was WAY oversized for my house. I presently have a two stage 90-140KBTU furnace installed. He said he would put in a 90KBTU and back it off to an 80KBTU. This got me to thinking so I decided to decrease the gas supply to my furnace by slightly turning the gas valve on the pipe feeding the furnace. Now I want to know this: What is the tradeoff in a high temperature rise versus a low temperature rise? Is one more efficient? Is one more comfortable? I have backed my fan speed down to the lowest settings and REALLY like how much quieter the unit is now too. Any help would be greatly appreciated.