With the "Send in the Guards rule" you are forced to take only one list (Core + Polish Lancers)in order to win a pick-up game battle.
French Guards need lots of Pursuit cav to win, they can only take them by taking Allies, the Polish allies being the best option probably. So, in a pick-up game with one support - or tourney game - the French Guards can only take thier core Young Guard plus Allied cav support with Pursuit in order to win decisively, otherwise they could only hope to win marginally(therefore lose). But now they don't even get to use a unit with the Guards attribute but are still hampered by the "send in the Guards" rule.
I read the optional for "small games" version of this rule in the Tips DL section.
"The Guard army wins if it breaks the enemy morale and either (A) pursues, or (B) holds the objective at game’s end."
It looks like it should work, but still requires a single living Cav unit left after you've broken your opponent's morale (for "A") as you must be able to pursue or gives you victory if you take the objective(B). Now, to me, it stands to reason that if I break someone's morale and thier army flees the field, cavalry or not, I ALWAYS will count as taking the objective since he is no longer there to contest it. Unless my opponent wants to watch me marching my armies across to the object solo play after he's picked up his units, he would probably concede to this logic.:)
It seems the optional "Send in the Guards" rule is at odds with the "send in the Guards" from the rulebook and even makes it so thay all Guards list have to do is "pursue" and they get the decisive victory! So this optional rule may make it easier for Guards to get a Decisive victory, which is not the intent of the SitG rule from the book.
So the point of my post is not to stir up trouble, but to point out that the Guards list probably don't need this confusing and at odds with itself rule in any version. Thier Army builder seems to be pretty restrictive on Pursuit Cav options and therefore very balancing. For instance, in a single support option game, French Guards can choose either Cav with no extra arty as reserve, Old Guard with no arty in reserve and a heck of a long way to march, or more Young Guard with arty but no Guard attribute (for which you are being penalized for) or you may take Core + Polish Allies.
The Guards Core + Polish Allies is really the only sensible option and will admittedly make for a great army, but - in a tournement at least - it will be far more common than it should be. No one will want to play a French Guards list with Core + Pol Lancers 3 games in a row...