I don't know of a 450W Corsair PSU, but their 430W PSU has 32A on the 12V rail meaning that it will support the 6870 (12.5A) but not the 7870 (40A). If you want a 7870 I'd get their 600W which has 46A on the 12V rail.
Thanks for the reply... I am quite happy about it as it will support a decent graphics card which can play all games... I got the review from this site and it seems like a pretty decent psu which can almost provide upto 500W... http://hardwareinsights.com/wp/corsair-vs450-review/