I have owned a Beech Baron 58P. I looked at the Cessnas for comparison when I purchased the Baron, but went for the Beech quality and handling. As far as operating costs, you can plan on around $250/hour, at least, for the Baron. A lot of the cost depends on where and how high you fly. Those Continental 520 engines can put out quite a bit of power--310 or 325hp for the post-79 models, but that power comes with a price tag. There are few 58Ps, or any aircraft with those engines that fly at the flight levels, that make it to TBO. They just run too hot and the air is too thin where you want to fly (eg: critical altitude). If you are constantly pushing the plane's ceiling, Cessna or Beech 58P, you are going to buy an engine overhaul at about half TBO. Altitude is not good for recips--and the Continental 520L is no exception--regardless of the graphic engine monitors you've got on board. When your TIT is running at 1600 degrees and you're flying at FL250 where the air is thin and doesn't cool effectively, there is metal fatigue--at the elemental level. You can't get around it. Were you to just fly below FL 180 all the time and wanted the pressurization just for comfort, you can get a longer engine life out of your plane.
The Cessna will be cheaper to repair--cheaper for parts, etc. The engines are the same. But, in my opinion, the Beech is much more sturdy--handles like a baby King Air. I didn't use it as a business aircraft, but as a personal one, and the 58P, if you can afford it, makes a great personal twin--comfortable for yourself and family, and it handles like a Bonanza.
Now, if you want a plane with a larger engine that would be more likely to go to TBO, and has comparatively almost the same operating cost as the Baron or Cessna, there is the Duke--and many people swear by them. They are cabin class, a Beechcraft, sturdy, and use larger, 380hp, Lycoming 560 engines which have a very good record of making it to TBO. Naturally (no replacement for displacement), the Duke engines aren't working as hard to maintain altitude and pressurization as the smaller Continentals, but they have a higher ceiling, too.
The Continental 520 series is known to require early engine work or a top-end, though operators will be quick to deny it or blame others' poor engine management. Chances are more likely than not that you'll be forking over $35,000 for that engine overhaul--if you fly the plane where it's supposed to be flown--by 800 to 1000 hours. So, budget for that, too.
I suggest you call Ron Knudsen at Willowbrook Air Associates in Englewood, Colorado about the cost/benefit picture of a nice, late model Duke for your business. You can find them at
www.aso.com/ as one of their featured dealers. Were I in the market for another pressurized twin, I'd look at the Duke. Then again, I've never liked twin Cessnas--310s, 340s, 414s, 421s or whatever.
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DJSchaut