splinters are great, but like blackwood, they're often abused. that they take up a lot of space doesn't mean you should quit playing them, but it does mean they have to be narrowly defined and used with discipline.
i wouldn't call a double of a 4 level pre-empt 'optional' in any position. by a passed hand it's a pure takeout double anyway - normally a void, especially as in this case where you're a passed hand too. with short hearts and no honours it's pretty clear pull for me.
partner shouldn't cue. a splinter (unless you're planning to bid on) should tell partner you need no wastage at all in the splinter suit. here 1/4 of the hand is down the toilet. aces in other suits are a mirage - responder is not expected to be short there. still, you did too much too.
i'd play x as penalties. with hearts, bid hearts. if you start with an amorphous double (where available) it's much harder for partner to bid game. getting to game is more important than getting to the right partscore.
who says 1d doesn't guarantee 4 diamonds? it does in walsh, though of course it may not in whatever system you play. anyway, it wouldn't need to guarantee 4d in the acbl. 3 would be sufficient to be non-alertable.