Alienware X51 with 22% discount (worth it now)

X51 with :
I3 2120 3.3 Ghz
6GB 1333 MHz
1 TB serial ATA
1GB GDDR5 GT 640
£450 Seems like good value to me, then again i know nothing compared to the guys here.
I have no clue as to the upgrade ability of the system.
How decently it would perform for my most played games, SWTOR, GW 2 Total War Series, FM 2013 and a few others.

Can have it with an
i5 3330 3.2 GHz / i5 3350 3.5 GHz
6 GB 1600 MHz / 8 GB 1600 MHz
£480 + £50 for 3350 + £30 for 8 GB

OR
i5 3450 3.5 GHz
8GB 1600 MHz
1.5GB GDDR5 GTX 660
£690

Advice on value, performance and a combination of both and finally other options for similar values?

Thanks C.