booze and cake
probably out cycling
There's loads of variables with this so I think making predictions is a bit a punt but its the internets so lets have a go anyway 
. The following just relates to my personal experience and I'm sure others may have conflicting opinions so please bear that in mind.
If bike fit is OK and all the contact points already mentioned have been through, fatter tyres is probably the cheapest option. There is also the frame geometry to consider, and the skill and blend of tubes used by the framebuilder, with slacker angles generally being more comfy.
In my experience carbon bars on the whole seem to take some of the buzz out but its a bit of a trade off. I had some Ritchey WCS carbon ones which flexed a bit which was a bit disconcerting at first but I got used to them and they were comfortable. Conversely I had some newer FSA compact K-force ones which did'nt seem to flex at all but and as a result were less comfortable, and you'd notice it on a 100 miler.
In my experience I think the flex issue with bars is similar with frames, I have ridden alu and found it a bit harsh, similar in feel to 520 cromoly which I was'nt really keen on.
I have a steel Reynolds 853 pro-team bike which I think is used for the main triangle and then has either 731 or 631 seat/chain stays and forks, this rides really nice but I know some consider 853 a bit too stiff for 100 milers.
But my favourite of what I've ridden (and there loads of different Columbus version I've never ridden so again I'm no expert) so far is a Columbus SL frame which is my go to frame for long rides. For me it has the perfect blend of flex to absorb bumps without feeling noodly, official techy term
I'm about 13 stone so if you are 14 stone of more maybe SL could be considered a tad too flexy, who knows?? I think the Columbus SLX version was stiffer. I think you get the gist thats hard to tell what is going to be good for someone else.
If it was me, (and nothing wrong with N+1 if you can afford it and have space), I'd try and hunt around for a 2nd hand steel frame or complete bike and try and have a test ride, though I appreciate this may not be possible. A 2nd hand frame/bike will be cheaper so if you don't like it you can sell it on without taking a big financial hit.
So all in all clear as mud good luck.
. The following just relates to my personal experience and I'm sure others may have conflicting opinions so please bear that in mind.If bike fit is OK and all the contact points already mentioned have been through, fatter tyres is probably the cheapest option. There is also the frame geometry to consider, and the skill and blend of tubes used by the framebuilder, with slacker angles generally being more comfy.
In my experience carbon bars on the whole seem to take some of the buzz out but its a bit of a trade off. I had some Ritchey WCS carbon ones which flexed a bit which was a bit disconcerting at first but I got used to them and they were comfortable. Conversely I had some newer FSA compact K-force ones which did'nt seem to flex at all but and as a result were less comfortable, and you'd notice it on a 100 miler.
In my experience I think the flex issue with bars is similar with frames, I have ridden alu and found it a bit harsh, similar in feel to 520 cromoly which I was'nt really keen on.
I have a steel Reynolds 853 pro-team bike which I think is used for the main triangle and then has either 731 or 631 seat/chain stays and forks, this rides really nice but I know some consider 853 a bit too stiff for 100 milers.
But my favourite of what I've ridden (and there loads of different Columbus version I've never ridden so again I'm no expert) so far is a Columbus SL frame which is my go to frame for long rides. For me it has the perfect blend of flex to absorb bumps without feeling noodly, official techy term
I'm about 13 stone so if you are 14 stone of more maybe SL could be considered a tad too flexy, who knows?? I think the Columbus SLX version was stiffer. I think you get the gist thats hard to tell what is going to be good for someone else.
If it was me, (and nothing wrong with N+1 if you can afford it and have space), I'd try and hunt around for a 2nd hand steel frame or complete bike and try and have a test ride, though I appreciate this may not be possible. A 2nd hand frame/bike will be cheaper so if you don't like it you can sell it on without taking a big financial hit.
So all in all clear as mud
good luck.
I do like to shop 
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