Long rides also beat up my contact points, my hands in particular (despite extensive use of tri-bars).
I know that the proper answer to this is to work on my strength and reduce my body fat percentage so as to get faster. And I promise to work at this, honest! But at age 66 and without an athletic gene in my body and having started Audaxing proper only six years ago, the chances of my making much headway at this are slim.
An interesting set of circumstances!
I'd say a lot depends on how important the sport is to you and how much you want to do it. It is a matter of choices, but perhaps not the ones you are thinking. The contact points are an issue not so much related to speed, so changing your bike to a laid back may potentially help - but you may also find that your current lack of speed/fitness makes you fight harder and compromise your form on long rides leading to the problems with contact points (rather than just the type of bike). You may even need to consider bike fitting, if you haven't already.
But the second bit quoted above is probably where the heart of this issue really lies.
You don't need to be genetically superior to ride well in Audax-type events and 66 years is not as old as you may think. I can assure you the easiest way to address the issue being described - and to lengthen your Audax life - is to build your strength. There are two ways to approach this.
1. You can do shorter rides at higher intensities and follow a more structured training programme approach to your cycling - rather than do every ride at comfortable and laid back pace.
2. By following a simple 30 minute full body strength training programme, twice a week, in a gym. By simply reversing the 'wastage' you have experienced in your muscles through increasing your strength, your cycling performance will increase tremendously - even if you don't lose weight.
I am a big believer in stength training for the full body, not just for sports but for essential physical well-being. Building strength throughout all your body's muscles is one of the most important ways YOU can slow the ageing process and remain younger for longer. It may be new to you but there is no reason it can't be enjoyable and you should not think of such exercise as intimidating. If you find a personal trainer they can give you a routine and show you how to follow a very simple and basic strength programme to suit your time demands. It doesn't have to take much time, it just needs to be a regular part of your life.
As much as we love doing the things we love doing, we have to accept there are small 'sacrifices' we can make to improve on the situation by simply doing a few additional things, to which we may not be so strongly drawn. It's about "doing things" and "doing things properly". If you like Audaxing perhaps consider making a few more changes and thus doing it better. You may have to 'sacrifice' a little more by changing things, but you'll also enjoy the rewards more and that will make the changes more worthwhile and more attractive.
You can't have your cake and eat it in the real world and you can't really 'cheat' through equipment upgrades. On average, people on recumbents don't necessarily do very much better than people on upright bikes in Audax events, even though we know recumbents will sometimes have definite (but small) mechanical advantages. I don't think riding a recumbent will change your outcomes in relation to pace. Only a change in your approach to training and preparation can do this.
I am certain the biggest impact will come from simply improving your strength and these changes are very fast to happen. Within 2 months of following a gym routine I guarantee your riding will have improved without changing anything else. And your weight will probably reduce somewhat as well, because of the changes in muscle density alone in combination with your normal riding.
I hope this is useful, please consider it?