Best WordPress Plugin to Speed Up

I searched a lot and spent more time to find the solution for speed up my WordPress site. computerpakistan.com But I found. WP Simple Thimble is really help me. let me share my problem

I was using http over my wordpress site. Everything working fine in it. When I transfer http to https my site down to 7 seconds from 1.8 seconds. I got confuse. I searched but no result come. I install this plugin and checked speed in xtmatrix said hurry!