Should I all pages use https? And if it's need to use VPS for Magento?

Hi dear masters:

I have set all pages use https but I hear from friends which https will make the page loading slower and some friends say register page and payment page use https is ok. I wonder listen to your idea because I know you are master. And if I want to set only register page and payment page use https, how do I set that, please? Our website is http://www.herawigs.com

We both know that Magento is too slow and we are trying to rush the speed and I hear that VPS is better to speed. Do you think it’s good to use VPS and do you have any good suggest for good VPS and have better price?

By the way, I find our demo of our website can’t open, do you know that?