4 by East	NORTH A 9 7 6 3 2 K 4 2 5 2 Q 4
WEST (dummy) K 8 5 Q J 9 3 A Q 10 A 5 2		EAST Q 10 4 A 10 7 6 5 9 6 4 9 7
	SOUTH J 8 K J 8 7 3 K J 10 8 6 3

To see what the proper matchpoint play is, let's divide this up into cases:

1. Suppose East calls the 10.
   Then East is 25% likely to make (if the KJ are with South), but 75% likely to go down an extra trick^* (if North has either diamond honour and gives South a second ruff).
2. Suppose East calls the Q.
   Then East is 50% likely to go down 1 (if South has the K), but 50% likely to go down an extra trick^* (if North has the K and gives South a second ruff).
3. Suppose East calls the A.
   Then East is 50% likely to go down 1 (losing one spade, one ruff, one club and at least one diamond), but 50% likely to go down 2 (by misguessing the diamond suit).

^*  Perhaps even more. See "Further Analysis" below.

1. At IMP scoring, East should put in the 10 because it is her only legitimate play to make the contract. If the play loses then East knows she is going down at least one and so she should make an effort to hold in the undertricks.
2. If, after South gets his first ruff, he continues clubs instead of diamonds, then East will be able to make 4 because she will have enough time to comfortably finesse twice in diamonds.
3. Suppose East plays the 10 (or the Q) from dummy and North wins the cheapest honour possible (i.e. the J (or the K)) and then gives South his second ruff. If South now continues diamonds, East still has a problem. She could rise with the A and try to guess trumps (resulting in down 3 or 4) or she could finesse her remaining honour (resulting in anything between down 2 or down 4, depending on who has the K (or J) and who has the K). These sorts of guesses are not much fun.

I guess that'll teach me for disobeying the fundamental rule of preempting:
    "Once you've preempted, your auction is over."