Looking for feedback (positive and negative) on upgrading of MarkV for combustion turbine control to Honeywell, Emerson Ovation or Siemens DCS systems?

Have you considered a MKVIe? since the MKV was provided with the OEM of the unit why not stick with the OEM for the retrofit? you will be able to get engineering support, ensure the settings/constants/logic is accurate, and have the large user base that uses MKVI's for Turbine controlling. I dont think the other DCS vendors listed is as experinced in primirarly Combustion turbine control and might not have the ability to model the bigblock logic hidden in the GE MK TCS.