Mark,

 

Most ES's are being built with either the IO-550N (310hp) or the TSIO-550E (350hp).  The only smaller engine I would consider would be a turbocharged TIO-360 or 390.  I'm based at 6,800 MSL and take off all the time with around 210hp.  The downside of installing another engine is the lack of support from the factory, engine mount, baffling, hoses, etc.  The two standard engines are easy installs with all the accessory kits available from Lancair.

 

Mike