Make WP_Query more efficient?

you can try some of these extra parameters:

 'update_post_term_cache' => false,
 'update_post_meta_cache' => false, 
 'cache_results'=>false,
 'no_found_rows' => true, 
 'posts_per_page'=>1,
 'post_status'='publish',

ps: you can measure the speed of your query when you are testing it with microtime()

http://php.net/manual/en/function.microtime.php

Edit:

Here is a another way:

function count_votes($user_id=1, $question_id=1, $post_type="vote", $meta_key='comp_question'){
    global $wpdb;

    $sql = "SELECT count(*) FROM {$wpdb->posts} INNER JOIN {$wpdb->postmeta} ON ( {$wpdb->posts}.ID = {$wpdb->postmeta}.post_id) WHERE ({$wpdb->posts}.post_author = %d) AND ({$wpdb->posts}.post_type = %s) AND ({$wpdb->posts}.post_status="publish" ) AND ({$wpdb->postmeta}.meta_key = %s) AND ({$wpdb->postmeta}.meta_value = %d)"; 

    // uncomment if you need to group it
    //$sql .= "  GROUP BY {$wpdb->posts}.ID"; 

    $count = $wpdb->get_var($wpdb->prepare($sql,$user_id,$post_type,$meta_key,$question_id));

    return $count;
}

and you can use it like this:

$user_id=1;
$question_id=1; 
$post_type="vote"; 
$meta_key='comp_question';

echo "votes: " . count_votes($user_id, $question_id, $post_type, $meta_key);

Edit 2:

Here is a function that returns an array of votes ids:

function get_votes($user_id=1, $question_id=1, $post_type="vote", $meta_key='comp_question'){
    global $wpdb;

    $sql = "SELECT {$wpdb->posts}.ID FROM {$wpdb->posts} INNER JOIN {$wpdb->postmeta} ON ( {$wpdb->posts}.ID = {$wpdb->postmeta}.post_id) WHERE ({$wpdb->posts}.post_author = %d) AND ({$wpdb->posts}.post_type = %s) AND ({$wpdb->posts}.post_status="publish" ) AND ({$wpdb->postmeta}.meta_key = %s) AND ({$wpdb->postmeta}.meta_value = %d)"; 

    // uncomment if you need to group it
    //$sql .= "  GROUP BY {$wpdb->posts}.ID"; 

    $ids=array();
    $ids = $wpdb->get_col($wpdb->prepare($sql,$user_id,$post_type,$meta_key,$question_id));

    return $ids;
}

you can use it like this:

$ids=get_votes($user_id, $question_id, $post_type, $meta_key);
print_r($ids);