For the cost of converting a P-baron or a Duke you could buy an older King Air C-90. I think the Duke conversion was over a million. The problem with these is maintenance on an orphaned plane (out of business on the turbine Bonanzas) and they are really endurance limited since they can only carry so much fuel. I seem to recall around 3.5 hours as being realistic. So, some of the speed advantage is countered by the need to stop for fuel.
The advantages are the extra speed and reliability of the turbine conversions. If you need one worked on, will the average mechanic know how it's put together with so few out there?
The turbine bonanza conversion also has a relatively low TBO on the props- I think 1000h. Then, think about a twin turbine and doing hot sections- the hourly cost will end up being pretty close to that of a King Air, a plane that has a ton more room and is well supported.
The turbine bonanzas are fast and still fly like a bonanza, but whether it's worth the additional outlay in maintenance and service need to be considered.