Hello! The best option is to use .co.uk on London servers. This is THE BEST option! Also - you can use plugins for improving your site's speed. For WordPress there is one called W3 Total Cache - Here it is: https://wordpress.org/plugins/w3-total-cache/ It is free and ones set up it will drastically improve your speed and overall performance! :-)
Here is another tutorial about improving WP plugin's performance - http://tutorials7.com/improve-your-wordpress-plugins-performance.html Hope that will help with your WordPress site's speed!