Windows is very slow with my new SSD

What you need to do, is to see what process is utilising your disk. Click on the Open Resource Monitor at the bottom of Task Manager. Then click the Disk tab and see what process is hogging up your drive, then post back here. This could be a number of issues from SSD Trash management to a rouge driver / app.

Also have same problem. I have Lenovo Z370 with OCZ Agility4 512 Gb. It was lightspeed fast on Windows7, but dramatically slow on Windows8.

I solved this problem by installing driver for Intel SATA AHCI Controller from default lenovo driver pack (D:\drivers\AHCI). Not need to make a clean install!

Now I like the benchmark results much more :)

*UPDATE*

It was nor Windows, nor SSD problem. It was an old BIOS firmware :) I have solved the problem for my Lenovo IdeaPad Z370 with the 4acn38ww64 BIOS update.
Readme says:

4acn38ww Fixed, When Resume From S3, HDD Translating Speed Becomes Low

And the issue seems to be cured, I am very glad :)

If you have formatted the SSD disk and reinstalled Windows 8 from scratch, letting it partition the disk, then I suppose that all partitions are well-aligned.

For Windows, check if the performance degradation also exists when booting in Safe mode. If it doesn't, then it is some installed non-Microsoft product that is causing the slowdown.

You could use the Task Manager to find the resources-hogging process.
See the article How to use Windows 8 Task Manager

You could verify your conclusions by either by uninstalling the product(s) or banishing them from startup by using autoruns.

Last, you could try to install the latest firmware for the SSD disk. As far as I could find on the weird patriotmemory website, these are the only available downloads, dating from 02/09/2012 (installation not recommended unless in despair) :

Torqx 2 TRIM Utility Beta Install Guide
Torqx 2 TRIM Utility Beta