Comfort and speed are not mutually exclusive. However, there is a point at which you are playing one against the other. In terms of frame materials, steel, carbon, aluminum and titanium can all be fabricated to create great bikes. It’s the way the material is used that makes for different ride characteristics. I think your best bet would be to go to a good LBS and tell them what you are looking for in ride characteristics and see what they recommend. I suspect they will steer you toward a comfort bike like the Specialized Roubaix or the Giant Defy. I’d be very leery of taking the recommendations of anyone who used phrases like, “Carbon is much more comfortable than aluminum.” Either they don’t know what they are talking about, think you’re a dolt, or have inventory they are trying to sell. In any event, it’s probably in your best interest to test ride as many bikes as you can in the comfort range. The one thing that concerns me is that even with the carbon comfort bikes, they are not going to have the long wheelbase/chain stays that a typical touring bike has. If this is a large part of why you like your current ride, you may be looking for a lighter and stiffer touring frame that will allow more of the pedaling energy to be effectively transferred into driving the bike forward. But lots of test rides will help you know.