It really depends (in Europe) on whether you have an IR.
If not, you are continually bound by controlled airspace.
If so, filing IFR makes CAS irrelevant and then a turbo is worth having. Unfortunately, few turbo engines make TBO - presumably because they are used as intended
However, considering a turbo without also considering anti-ice equipment is misguided. I don't have a turbo but my TB20 can go to 20,000ft (ISA conditions, or colder) and that is good enough for practical IFR, done as VMC enroute.
If you make a case for a turbo being able to get you through freezing layers, you are taking a bit of a chance on getting stuck in icing conditions for extended periods, and a turbo alone (i.e. being able to climb to say 15000ft at +1000fpm) isn't going to do you much good for the next few hours in level flight.
The extra ceiling due to the turbo (typically 25k v. 20k) cannot be realised without using oxygen masks (not just cannulas) and while cannulas are easy and hassle free (I've done 2.5hrs today with one up my nose
and up to 7hrs on other occassions) the same cannot be said for masks; nor for the much higher oxygen usage which raises topping-up issues.