Beguiler, Warmage, and Versatile Spellcaster

[Chambers]

Okay, back at my books. Doesn't look like it works for the Beguiler in terms of RAW.

Spells:A beguiler casts arcane spells, which are drawn from the beguiler spell list on page 11. When you gain access to a new level of spells, you automatically know all the spells for that level on the beguiler spell list. You can cast any spell you know without preparing it ahead of time. Essentially, your spell list is the same as your spells known list.

I figure that's the relevant text. The second bolded part supports your idea, but the first bolded part works against it. If you are a 6th level beguiler you haven't gained access to 4th level spells and thus you haven't learned all the spells for that level. So until you actually gain access to that higher level of spells you do not know them.

How's that sound?