Oxygen above 20,000 feet

If you're thinking about going from an Arrow to a T-310, I hope you've also
thought about burning 30 gallons an hour and the need for recurrent
multiengine training as well as the management of turbocharged engines.

A T-310 may cost $300 an hour (at least compared to my Baron), and there
have been some expensive ADs on the twin Cessnas regarding the exhaust
systems (as I recall).

You should also strongly consider a ride in an altitude chamber to be able
to recognize the signs and symptoms of hypoxia, which can be insidious.

The transition from an Arrow to a T-310 is a pretty big jump in cost and
complexity.