Its not about bending the mast to the Nth degree, its about having a reliable offshore rig since the OP says that he is buying a Calber 40LRC. The long range cruising models were optimized for offshore and long range cruising where the convenience of not having to raise a mainsail seems pretty trivial when you consider the need for fast, accurate and reliable reefing, (per RichH), shortened sail life implicit with in-mast furling, and that as a long range cruiser the mainsail will be up for weeks at a time without having to raise or lower it.
The spar stiffness issue is one of safety. Most rigs, even the comparatively stiff rigs of the 1960's and 70's, will sag to leeward in a abig gust and with the head of the mast curved off off to leeward in a really big gust. Even a small amount of sag and flex will help depower the boat noticably in big gusts and the added stiffness that is often designed into rigs with in-mast furling takes away that flex.
I would also suggest that in-mast furling is a poor choice for a single-handed sailor going offshore. If the in-mast furler jambs, as they tend to do more frequently after long periods reefed under high load, a single-hander does not have the crew to assist in freeing it through the various methods recommended which often involves sending someone up the mast to clear the jambs.
I can understand that to the current generation of arm chair sailor, weekend warriors, in-mast furling may seem appealing, but for the Original Poster, who is buying a boat that is heavily biased for offshore work and long distance voyaging (to the point that they make lousey daysailers and coastal cruisers) in mast-furling should be a deal breaker.
For what it is worth, many boat builders who had previously been making in-mast furling standard (charging an up charge for a normal mainsail) on smaller and smaller boats have begun to move away from in-mast furlers as standard equipment. I asked about this at the last boat show and was told that the service calls were killing them and besides they were feeling a real push back on this issue.
Then again, I should have known that you would defend anything that hurt sailing ability, seaworthiness and performance.