As promised I tried to lay out what the differences are between gestalt and multi-classing.
Gestalt class versus multi-classing
HD – best of the classes being combined. {This is different than multi-classing since you get both hit die which increases the ECL of the character}
BAB –best of the classes being combined. {This is different than multi-classing since you add both classes’ BAB to find out the character’s BAB}
Saving Throws – combine best of both classes being combined {This is different than multi-classing since you add both classes’ saving throws to find out the character’s BAB}
Weapon and armor proficiencies - combine both classes being combined weapons and armor proficiencies. {This is the same as multi-classing}
Class Skills – all skills of each class are treated as class skills {This is different than multi-classing. While both are considered class skills for max rank purposes, determining the cost (i.e. whether they cost 1 sp/rank or 2 sp/rank)
Skill points – best of both of the classes being combined. {This is different than multi-classing since you treat each level as different.}
Class abilities – character gets all class abilities of both classes being combined, except for those that are the same (e.g., uncanny dodge, turn, etc.) which advance at the best rate. {This is different than multi-classing since each advances independently, unless otherwise specified (like uncanny dodge)}
Class requisites (or prerequisites) – must be met for each class being combined regardless of the other class. {This is the same as multi-classing.}
Class restrictions – apply regardless of what the combination is. {This is the same as multi-classing. (Whether the gestalt is treated as a “single” class or not is moot for this comparison, although if treated as a “single” class it would make it different.)
So of 9 different parts:
3 are very different (HD, BAB and saving throws)
3 are at least slightly different (that is not the same) (Class skills, skill points and class abilities)
3 are the same (weapon and armor proficiencies, class requisites and restrictions).
So the question is how many similarities are required to consider something "similar" or "mostly" different?