As per Ken's advice, setting the font manually in the awakeFromNib() method gives the correct result.
You can either set the font property of the NSTextField
[self.myLabel setFont:[NSFont fontWithName:@"Lucida Grande" size:50.f]];
or use an NSAttributedString
NSDictionary *attributes = @{ NSFontAttributeName : [NSFont fontWithName:@"Lucida Grande" size:50] };
NSAttributedString *text = [[NSAttributedString alloc] initWithString:@"Hello" attributes:attributes];
[self.myLabel setAttributedStringValue:text];
Interestingly, in many cases I have seen fonts with spaces in the font name input with dashes, i.e. @"Lucida-Grande", this actually breaks the output, dashes must be omitted.