I have a Optiplex 990 SFF. Recently updated BIOS to A15 and I wanted to install Windows 8.1 x64 with the UEFI BIOS (Supposedly it boots very fast like that). 

Anyhow, I partitioned all drives as GPT, yada yada and it was all set up and running Windows 8.1 on UEFI with all drivers installed.

The thing I noticed was that Booting Windows 7 on legacy BIOS was so much faster. I have an SSD too but I am not sure why it is doing this. If I am not mistaken, UEFI boot means it will boot with the Dell logo showing and the spinning circle right? It doesn't show that, it shows a dell progress bar then boots into windows with the windows spinning circles.