Way to store featured image width and height in two separate variables?

You can always use the wp_get_additional_image_sizes() function to retrieve an image “size” (i.e. width, height, and the ‘crop’ option), like this:

$image_sizes = wp_get_additional_image_sizes();
if ( isset( $image_sizes['slide_image'] ) ) {
    $size = $image_sizes['slide_image'];
    var_dump( $size ); // Demo
    echo $size['width']; // Demo
}

UPDATE

In reply to your comment,

i want to get the current post featured image width and height..how to
do it

Use the wp_get_attachment_image_src() function:

The returned array contains four values: the URL of the attachment
image src, the width of the image file, the height of the image file,
and a boolean representing whether the returned array describes an
intermediate (generated) image size or the original, full-sized
upload.

— More on https://developer.wordpress.org/reference/functions/wp_get_additional_image_sizes/

But anyway, try this function:

// See https://wordpress.stackexchange.com/q/301465/137402
function my_wpse301465( $image_size, $post = null ) {
    $post_thumbnail_id = get_post_thumbnail_id( $post );

    $info = $post_thumbnail_id ?
        wp_get_attachment_image_src( $post_thumbnail_id, $image_size ) : null;

    if ( $info ) {
        $sizes = wp_get_additional_image_sizes();
        $size = isset( $sizes[ $image_size ] ) ? $sizes[ $image_size ] : null;

        return $size ? (
            $info[1] < $size['width'] ||
            $info[2] < $size['height']
        ) : false;
    }
}

And here’s how you could use it:

// Or pass a post ID as in my_wpse301465( 'slide_image', 123 ).
if ( my_wpse301465( 'slide_image' ) ) {
    echo 'Hide featured image.';
} else {
    echo 'Show featured image.';
}