Sneaky squirrel Xmas upgrade for the other half

Ok, The Gf is getting a few upgrades as part of her christmas box this year,
I'm finally getting her main Pc onto Win7 64bit so I'll throw that onto an Ssd (Dabs.co.uk are doing Intel 180Gb's for ninety quid)
and she will be getting my 975BE (that will be running at stock)
and maybe upgrade her to 8Gb of ram,
thats all pretty much decided but where I'm a bit unsure is this,
Do I give her my old 5770 to crossfire with hers or get a newer card (7770 maybe?)
either will involve a better Psu so I'll probably get a Cx600 anyway to power it whatever I do,
One monitor at 1440x900 Vga
So, new single card or crossfire the old?
(I'm thinking single card as her mobo is 16/4 on crossfire btw)

As it was brought up in a response I'd just like to say there will be no overclocking on her rig at all, not the Cpu, and not the graphics card, She's not a clocker and its non-negotiable, Gods know I've tried :)

Cheers guys, I know you are here when I need you :)
Moto
 
I was planning on that but in addition to the other improvements as well,
Win7, £70ish
Ssd, £90
Psu £45ish
Cooler £20ish
Gfx card (Assuming buying single 7770) £70
The cheapness of ram isn't an issue really its just further cost on top and this isn't her main gift, this is stocking fillers :)
its more the card issue I was vexing over though and I am more inclined to go single card
I just wanted some more up-to-date opinions on it so thanks for adding your vote man :)
Moto
 
Overclocking anything in her rig is not an option, I should've mentioned that in the op,
which is why the 975 is going to be at stock instead of 4.5GHz :)
Hwer Psu isn't as good as it could be anyhow so I was treating her to a decent unit,
it just seems sensible to do all these mini-upgrades at once,
What card would you have suggested then?
Say £150 max, preferably around £100 though
Moto