Can anyone help me with comparing two computers? Bit of math and am crap at it.

[Ray_Rogers2109]

I'd like to do a comparison of my current Compaq pre-built computer with the one I'm building. The Piriform Speccy image is of course for the Compaq with cheapo graphics card. The listing will be the fully completed computer.
How much of an increase in performance, in percentages maybe, will the fully completed computer be?

Currently being used pre-built Compaq. The ATAPI is the only physical drive and the rest are virtual.

Currently being built computer.

Operating System - Windows 7 Ultimate 64-bit
CPU
RAM
Motherboard
Monitor (sometime)
GPU (But unlocked to 6970.)
HDD (1 of ?)
Optical Drive

Thanks everyone who helped out with the comparison of the two. I'd just like to see how better the computer I'm building compares to my Compaq.

 

[jonnyp11]

so you already have these parts and cannot replace them, just asking, but the new one should eat the other for breakfast, but what about the power supply, and the os disk.

 

[Ray_Rogers2109]

so you already have these parts and cannot replace them, just asking, but the new one should eat the other for breakfast, but what about the power supply, and the os disk.

Oh the notes mean finalised specs of what I'm buying/set-in-stone/did the research months ago/etc. but the GPU and Monitor will still be bought but not immediately in September.
Well I haven't aten breakfast for months but how about for brunch?
the pre-built is a Compaq Presario SR5510F. The Power Supply is an hec Zephyr Bronze Plus 750w for the computer I'm building. August will be buying the CPU and RAM, possibly the USB 3.0 enclosure. September will be the optical drive and another Spintpoint F3 then setting up the operating system. Then afterwards, getting the dedicated GPU and monitor. New keyboard and mouse are luxuries.
I'd just like to see how much of an actual increase the new computer when fully completed will be in comparison with the current in terms of ratios/etcetera. I know it'll be far more powerful but I'm wondering, by just how much though? From a technical standpoint.
Neglected to mention I'll eventually be having 16GB of RAM with another of the same exact RAM cards.

EDIT: Just looked on Compaqs website and the computer I'm on now has a 250w PSU. What a joke!

So how much overkill is the computer I'm building in comparison with the Compaq?