I have a turbocharged Subaru 6A. The turbo is worth about 10-15 extra knots at 10-12,000 feet. To get the bigger gains, you need to suck on oxygen and get up to 18,000+. This is a pain and you need an IFR rating above 18,000. If you don't want to go through the oxygen thing, probably not worth it.
Engine cooling in the climb at high density altitudes may be an issue even with a Lycoming and you'd need an intercooler as well. This will add extra cooling drag, weight etc.
Big advantages are if you fly from high elevation airports or in the mountains in climb performance but a 200hp Lyc with C/S prop gives pretty decent performance up to 10-12K anyway in an RV.