Well, if not actually "rules" then guidelines:
1] Tenon length [projecting into the breadboard] as a proportion of breadboard width?
2] Given answer to item 1 above, anything other than tenon length/breadboard support inherently wrong with a wide [6"] breadboard, as opposed to narrower [3" - 4"]?
3] Max width [running along the edge of the table] of an individual tenon? [I understand the need to allow for wood movement in mortise design - that's not really my question].
4] Total amount/percentage of table width that should remain behind as tenons after the sawdust stops flying? Or, conversely, how much table should be removed between tenons to maintain structural integrity between the breadboard's mortises?
5] Would drawboring the pins through the slots in the outer tenons create too much friction for the tabletop movement to overcome? Well, without making splinters fly - I know you can't stop the top from moving, I'm just wondering if drawboring would cause the pins to bind, and buckle/break.
If it matters - table top will be QSWO, 42" wide, 1" thick [maybe up to 1-1/4", but I'm thinking 1"].