Found this post on another public forum and seemed lots of good info in a short space.
GLASGOW GUIDE DISCUSSION BOARDSAUG 2007MSG 175 Paul Kelly wrote
The following surnames are all commonly found in Ulster and I have discussed them in previous posts: McHugh/McCue, McCoy/McKay, McKee and McGee/Magee. These surnames are often confused with one another and I would like to clarify a few things.
The McHugh/McCue surname is a native Irish surname originating in west Ulster and is common in County Donegal.
The McCoy/McKay surname is commonly found in east Ulster, particularly County Antrim. Some of the Ulster McCoys/McKays are descendants of 15th century Scottish Catholic McKay Galloglasses from Kintyre and Islay while the other Ulster McCoys/McKays are mainly descendants of 17th century Scottish Protestant McKay Planters from Kintyre. McCoy is the Irish spelling of the Scottish surname McKay and both forms of the surname are found in Ulster.
The McKee surname is commonly found in east Ulster, particularly Counties Down and Armagh. The Ulster McKees are mainly descendants of 17th century Scottish Protestant McKie Planters from Dumfries and Galloway. McKee is the Irish spelling of the Scottish surname McKie which originates in Galloway.
The McGee/Magee surname is common in both east and west Ulster. The McGee family of west Ulster (Donegal, Tyrone and Fermanagh) is a native Irish family. The Magees of east Ulster (Antrim and Down) are mainly descendants of 17th century Scottish Protestant McGhee Planters from Ayrshire and Galloway. McGhee is a Scottish surname originating in Galloway. The McGhee and McKie families of Galloway are said to be related.
Most of the 19th century Irish McCoy and McGee/Magee immigrants to Scotland had their surnames recorded in the Scottish forms of McKay and McGhee.
There has been some intermingling of all the above surnames because of the many movements of families between Scotland and Ireland.