If you are in the market for a new psu, here are some thoughts:
1. Buy the capacity you need and then some.
Here is a link to what you need; it depends on the graphics configuration:
http://www.realhardtechx.com/index_archivos/Page362.htm
I have no problem overprovisioning a PSU a bit. Say 20%.
It will allow for a stronger future graphics card upgrade.
It will run cooler, quieter, and more efficiently in the middle third of it's range.
A PSU will only use the wattage demanded of it, regardless of it's max capability.
2. Buy only a quality psu. Try to buy a tier 1 or 2 unit from a list such as this:
http://www.tomshardware.com/forum/id-2547993/psu-tier-list.html
Seasonic is generally very good.
Look for a unit with a 7 to 10 year warranty.
A good psu is a long term investment.
A cheap PSU will be made of substandard components. It will not have safety and overload protections.
If it fails under load, it can destroy anything it is connected to.
It will deliver advertised power only at room temperatures, not at higher temperatures found when installed in a case.
The wattage will be delivered on the 3 and 5v rails, not on the 12v rails where modern parts
like the CPU and Graphics cards need it. What power is delivered may fluctuate and cause instability
issues that are hard to diagnose.
The fan will need to spin up higher to cool it, making it noisy.
A cheap PSU can become very expensive. if it should fail.
Do not buy one.
3. It is unlikely that the price premium paid for gold rating will ever be returned to you in electricity cost savings.
There IS value in higher efficiency in that the cooling fan will need to run less and the unit will generally be quieter
4. Modular costs more. Consider that you are likely to be using most of the power leads regardless. There will normally be a decent place to store unused leads away and out if sight or the cooling airstream. Also, if you have a length restriction, the leads that plug into a modular psu will not bend as much as a fixed attachment consequently taking more room, not less.