I am interested in buying a Sapphire Radeon HD5770 1GB DDR5 VAPOR-X OC Edition Lite. I have built a system on the basis that i was going to get a GTS450. My PSU is CoolerMaster 460W (actual output 400W) with 18A on each of the two 12 rails. Should i stick with the GTS450 or can i go with the 5770 (knowing that a PSU upgrade is out of question)??
It's interesting to note that Sapphire's website says that a PSU of 500W is required for the 5770 (Vapor-X and regular) whereas Nvidia's site says 400W required for the GTS450.
However, on several online PSU calculators i've used, i always get the opposite result: 5770 requires less power than GTS450 (both tried with the same set of hardware: i3 3 Ghz, regular mobo, 2 x 2GB DDR3, 2 Sata HDDs and 2 DVD-RW).
Sapphire and other companies are generally conservative as to the power requirements because they do not know what kind of PC you have. For example, you may have an i7-950 CPU while someone else has an i3-550. The i7-950 uses more power and would therefore need a more powerful PSU.