I'm thinking about fielding Pegasus Knights tomorrow for a 1k points battle (in fact, it will be 1150 points because of our campaign rules), and I'm really curious about how they'll work. It seems really nice to me, especially when combined with Enchantress with Ring of Magic (Lady's favour cast without a roll) for outflank.
Peasants with Grail Reliquae is a must-have choice for me. Against armies with strong shooting, I just send them forward to catch all the shooting. They're not driven back or confused (so the shooting doesn't break your formation) which makes them excellent meat shield. Against other types of armies - 4 attacks for such a low point cost is great. And it's a unit that you don't mind getting rid of in a suicidal charge, just to weaken stronger enemy units. Although, when it comes to compulsory charging the enemy, it's kind of hard to arrange them so all the units are touching the one with the relic. And pursuit - that's not something you would do unless the unit with the relic itself is in the combat (I try to keep it behind as long as possible). As I said, brigade of 4 peasants with grail reliquae is a must-have for any Bretonnian general.
However, I usually don't maximize number of knights in my army. I like to have decent number of troops to drag the enemies out where I want them, and to have an "anvil" smash the enemies against with my cavalry. The disadvantage of this approach is low break point (2 for 1k points, 3 or 4 for 2k points), so you have to be extra careful where you're sending your precious knights.
Trebuchet - I decided to scratch build one for myslef, but I'm probably not gonna usi it untill I have 2 or three of them (so they can actually cause casulties). I don't like the idea of unmovable machine which forces a highly mobile bretonnian army to guard the warmachines.
It's WIP, but the construction itself is complete. Now, I "only" need to paint it, convert the crew (peasants seem to be the best, because it's probably the only unit that doesn't have shields) and make the base.
