Well it sounds like you’ve
Well it sounds like you’ve already ruled out the Cervelo and the the reasons you give are the right ones – if you’re not confident about cutting down the steerer don’t do it (on the other hand maybe you could get your lbs to do it for you?) plus spending that amount of money on a bike you cannot try is a bit of a gamble even on something as good as the Cervelo.
The best bet would be to try both the bikes – the Cannondale is a tasty, okay very tasty bike… and with Cannondale you generally get a lot for your money these days, but titanium is special. I’ve only every seen one Sabbath bike and I’ve never had any dealings with them, but the guy testing it thought it was a peach.
In the past I’ve asked most of the bike journos I know what type of frame material they would chose if they were spending their own money and in most cases the answer is titanium – it lasts.
Don’t let that sway you though – go and try the bikes!