Everything i have read says the 450 is the better card and its cheaper than a 5770 as well.
I refused to buy a 5770 on price alone as it was over priced at launch for what it is.
A decent 5770, by which i mean something like the MSI hawk will in the UK cost you about £135. The ASUS top 450 which is a better card than the MSI Hawk will cost about £117.
However the issue that causes the most problems when looking at the top performing 450/5770 cards is that the 460 768mb card can be had for less than £10 more.
The stock cards are obviously that bit cheaper with the 450 around £95 while the 5770 is more like £110 again price would sway me to the 450.
Obviously thats just based on a UK price point but thats where i am so thats what i can use.
Mactronix