The biggest plus in gx for me is the hybrid fan mode (less dust)
First, both have fan control. The fact the GM does not support fanless mode is really of very little significance - unless this computer will be used in a high-end HTPC (home theater PC) and in a home theater environment (that is, a room designed to dampen and suppress ambient and outside noises).
If being used for other than HTPC tasks, with a good case (I like Fractal Design cases), you won't hear the fan anyway. And with a good case, even if the GM fan is spinning at its "silent mode" (slowest) speed, the amount of dust it pulls in will be negligible compared to the normal case cooling fans. If you set up your case cooling properly and have a good case, dusty incoming air will be pulled through the air filters - a good thing. So, unless you live next to a dusty rock quarry, you always keep your windows open, you have several dogs and cats shedding pillows worth of hair and dander every day, and you have a couple rugrats running around keeping all that stuff stirred up, I would not place much value on the fact one has hybrid mode and the other does not. In other words, it is good you are concerned about dust control, but in this case, those concerns are unnecessary - or at least should not be that big of a concern to be "the" deciding factor. Dust control is the responsibility of the case, not the PSU.
And please note, this is from a guy who
really hates fan noise!
the fan has only 25,000 hours of life and within 5 years i will reach this number.
How did you determine that? First, the 25,000 hour rating does not mean in 25,001 hours it is going to die. Also, that is at 40°C which means that PSU would be running at "very very warm" temps the entire time. Unless folding or mining, that is not likely. Also, verify your math. To reach 25,000 hours in 5 years, that computer would have to be up and running running fairly demanding tasks (not just at idle) almost continuously 14 hours each day, 365 days per year for 5 years straight (13.7h x 365d x 5y = 25,002.5 hours). Finally, the supply has a 7 year warranty. If the fan wears out in 5 years, get a new supply for free under warranty.
That said, the Focus has a 10 year warranty.
Most people buy way more power supply than they need. 550W is probably plenty but you have not listed your total specs. So you really need to sit down and figure out, as best as possible, what your needs will be in 2 or 3 years. Don't guess. You can research each and every component to determine their maximum demands, add them up, add a little for inevitable aging to get your needed size. Then pick your supply.
Or use a good PSU calculator to do all that for you. I only use and recommend the
eXtreme OuterVision PSU Calculator. This will calculate your minimum needs and recommend a suitable size for those needs.
Plug in all the hardware you think you might have in 2 or 3 years, to include extra drives, bigger or second video card, more RAM, etc.
I recommend setting CPU utilization to 100% and Computer Utilization Time to 16 hours per day. These settings will help compensate for component aging, and add a little extra padding to the results. This will also result in a little cooler and quieter operation.
Note that no calculator wants to recommend a PSU that is underpowered so they all pad the results, some more than others. The eXtreme OuterVision calculator is and can be the most conservative (my reason for using it) for 2 main reasons. (1) They have a team of researchers on staff constantly researching components for us to keep their extensive databases accurate and current. And (2), it is the most flexible and has the most extensive databases of available options you can enter. This allows it to factor in all possible components to accurately calculate our needs rather than guess.