Graphics upgrade?

OK so I have some fairly hefty constraints on what I can upgrade my ageing Shuttle PC with.

First and foremost is power constraints with only a 450W PSU in the case ...
Then comes dimensions...With a precarious motherboard power connected in the lower left. I barely got my GTX 275 in there!

http://www.tomshardware.com/reviews/geforce-gtx-275,2266-14.html

http://www.nvidia.co.uk/object/graphics_cards_buy_now_uk.html

I'm thinking this Zotac will fit the bill in terms of size and power draw.

http://www.ebuyer.com/393783-zotac-gtx-660-ti-2gb-gddr5-dual-dvi-hdmi-displayport-pci-e-graphics-zt-60801-10p