Help! will my build be able to run a Radeon HD 6770 graphics card?

Hi,
I a Noobie PC builder and I'm looking at investing in a nice, yet affordable gaming video card for my PC ($100-$150 range). I have been looking at the Radeon 6770 graphics cards particularly because they appear to be the best within my budget without needing to make any alterations to my current build. It looks like everything checks out compatibility wise with my motherboard, but one thing that is concerning me is that I'm afraid my power supply (460w) will not be sufficient enough to run all of the components. AMD's website stated the system requirement to run the HD6770 is at least a 450w power supply. Would it be better to buy a slightly lower end card without sacrificing too much quality? or would it just be best to invest a little more and upgrade both my PSU and video card? ( P.S. I obviously don't need the nicest video card on the market, but I would like to make the most logical decision based on my given situation)

Here's the main components in my current build that I have to work with:

CPU: AMD Phenom II X6 1055T Thuban 2.8GHz Socket AM3 125W Six-Core Desktop Processor

MOTHERBOARD: GIGABYTE GA-880GM-USB3 AM3+ AMD 880G HDMI USB 3.0 Micro ATX AMD Motherboard

(CURRENT) VIDEO CARD: SAPPHIRE Radeon HD 5450 1GB 64-bit DDR3 PCI Express 2.1 x16 HDCP Ready Low Profile Ready Video Card

RAM: GSkill DDR3 4GB X 2 (CL 9-9-9-24, 1.5V)

PSU: COOLER MASTER Elite 460 RS-460-PSAR-J3 460W ATX12V V2.31 Power Supply

DVD/CD DRIVE: Optiarc DVD RW AD-7260S ATA Device

HDD: Seagate Barracuda ST31000524AS 1TB 7200 RPM 32MB Cache SATA 6.0Gb/s 3.5" Internal Hard Drive -Bare Drive

Thanks!