[Zorono]

great web design is a must . but dont forget the user experience . good web desing need a great user experience of using it . make the design that is easy to use and can give the user great experience .

but some of the great design really slow old device down espescially the website that have lot of heavy css and javascript

Agree with you but minifing the template's source (CSS, JavaScript...) Could solve this problem but at first there must be some optimise... Use MySQL as your Main Database saving/loading module as it's the fastest module on my opinion...