Upgrading 2 fans and Heatsink Dell XPS 9100

I currently have a Dell XPS 9100 w/ Gigabyte 6870, Intel i7 920, and 20GB RAM. I just purchased the Cooler Master Silent Pro Gold (SPG) 800 Watts Modular Power Supply. Why bother upgrading? Because 1366 is becoming old and I dont want to buy a new motherboard and processor.

Im not looking at upgrading my heatsink, rear, and front fans.

Rear Fan
I think these are the specs for my existing rear fan
Dell HU843

3 x 3-inches (80 mm)
2400 RPM fan speed
44.0 CFM maximum air flow
32 dBA noise level
3-pin connector

1. How come if the fan is 3x3 (80mm) it is still considered a 92mm fan?
2. I was looking at SilenX EFX-09-15 92mm Case Fan but it has 2 cfm less and the inside of my case does get very hot. I'm hoping the new PSU helps prevent heat build up.

What do you recommend? It does get pretty loud even if im not gaming or doing cad work.

Front Fan
My front fan I think is 120mm and mounted on a bracket. I'm assuming I can replace just the fan.
I see this auction and im not sure what the part number is for the fan and which one if for the bracket.
Dell Studio XPS 435T 9000 9100 System Cooling Fan AFB1212H M765N

I think the fan specs are Cooling Fan-AFB1212H-R00, 3pin Connector, 120x25mm, 2500rpm, 82.67cfm, 12V, 0.35Amp,

What would be the best fan with a higher CFM and lower dBA?

Heatsink
I was thinking of going with the
Noctua NH-U9DX 1366 Dual Heat-pipe SSO Bearing Quiet CPU Cooler

How do I know if I have a back plate without tearing my pc apart?


Here is the stock one.
I think I have a backplate because the four screw in the factory one.

Any recommendations on any parts would be much appreciated. I really want my computer to remain cool and quiet. I hope the new PSU helps prevent heat buildup over the existing 550w.