According to men's fashion maven Alan Flusser, the difference between "formal" and "semi-formal" evening wear is in the cut of the jacket and colour of the tie. White bow tie and tails coat are formal evening attire, short jacket and black bow tie are "semi-formal" evening attire. When the level of formality of an evening event does not rise to either formal or semi-formal, the fall back position is a dark suit, white shirt, and dark long tie. So, how does this equate with Highland evening attire? Like this:

FORMAL (white tie): Doublet or Coatee; wing-collar shirt; white tie (or jabot, depending on the jacket), white waistcoat (tartan is also acceptable); silver mounted sporran (hair or fur), and silver accessories (kilt pin, buttons, etc.); patent leather shoes with buckles; tartan or diced hose, and kilt.

SEMI-FORMAL (black tie): Doublet, Coatee, or Jacket; evening shirt with fold over collar; black bow tie, black, dark coloured, or tartan waistcoat; full mask or silver mounted hair or fur sporran (brass mounted, especially if an antique, is also acceptable); silver accessories (kilt pin, buttons, etc.); well-polished black, lace up, dress shoes (not ghillie brogues); dark coloured hose, tartan or diced hose, and kilt.

LESS-FORMAL (dark suit & tie): Argyll jacket or similar with plain or silver buttons (black barathea is the preferred fabric and colour); white dress shirt with fold over collar; conservative long tie, and high buttoned waistcoat to match the jacket (a dark coloured or tartan waistcoat is also acceptable -- a dirk belt may be worn instead of the waistcoat); full mask or silver or brass mounted hair, fur, or leather sporran (the "Rob Roy" type of sporran is probably best avoided with evening attire); silver accessories (kilt pin, etc.); well polished black, lace up, dress shoes (not ghillie brogues); dark coloured hose, and kilt.

If you look at the above guidelines it's pretty obvious that a full mask sporran is the most versatile, as is a black Argyll-cut jacket with two waistcoats. You can also get away with a brass mounted sporran, provided it has a black bag, or one of fur or hair.

It really comes down to deciding how often you are apt to require formal, semi-formal, or less formal evening attire and, based on the above suggestions, buy the sporran that will give you the most mileage.