Alienware 18 BIOS Questions X21

Guys,

I have a Alienware 18, i7 windows 7, 16 RAM etc. 

My BIOS shows up as X21.  When I go to the download site to update the chip-set (completed) and the BIOS, it only shows up AW18A05.  When I go to install it the installer states

"Dell does not recommend that you flash your BIOS to a previous version."

even though the new BIOS is from this month, and the current one is from Mar 2013

So here is the question, 1. What is the most current BIOS for the Alienware 18 here is the info for it below from msinfo32

OS Name    Microsoft Windows 7 Home Premium
Version    6.1.7601 Service Pack 1 Build 7601
Other OS Description     Not Available
OS Manufacturer    Microsoft Corporation
System Name   
System Manufacturer    Alienware
System Model    Alienware 18
System Type    x64-based PC
Processor    Intel(R) Core(TM) i7-4800MQ CPU @ 2.70GHz, 2701 Mhz, 4 Core(s), 8 Logical Processor(s)
BIOS Version/Date    Alienware X21, 3/13/2013
SMBIOS Version    2.7
Windows Directory    C:\Windows
System Directory    C:\Windows\system32
Boot Device    \Device\HarddiskVolume2
Locale    United States
Hardware Abstraction Layer    Version = "6.1.7601.17514"
User Name   
Time Zone   
Installed Physical Memory (RAM)    16.0 GB
Total Physical Memory    15.8 GB
Available Physical Memory    12.8 GB
Total Virtual Memory    31.6 GB
Available Virtual Memory    28.4 GB
Page File Space    15.8 GB
Page File    C:\pagefile.sys

Secondly what is X21, and which should I be using?