You asked for experienced advice. So here it is: I bought and returned the costco gen set. I also bought and returned a Sam's club genset that had the Subaru-Robins engine and a 30AMP circuit. Neither were Chinese. Both are loud. You won't find noise ratings on them because they arent quiet. Quieter than a 454 chevy running open headers - maybe. I know quiet isnt an issue for you - but bottom line is, they are so loud it is uncomfortable.
2nd Issue - Clean power. In order to get clean power out of a generator, you have to have one that has filter/inverter capability. They give you a clean digital sine wave. The Link I posted shows on a graph the difference between clean and dirty. It is the difference between 18-20% distortion and 2.5% distortion.
I run lots of delicate electronics off of my Kipor - plugged directly into it, or into my camper. Laptops (toshiba and a gateway), my iPod, my digital camera, a portable hard-drive, DVD/TV, the list goes on....
To get clean power you have to get an a genset with a digital inverter.
All the ones Costco/Sam's have are lots of power, but no cleaner than what you have. more does not equal clean. If clean is a NECESSITY - than you have anywhere from 1000W up to 6500W gensets that have the proper filters/inverters to give you clean power.
They cost more than the cheap power you get from a Costco unit. A honda can cost you $2000. A Yamaha $18-2200., The Kipor comes in at roughly $1200 ( I sent you to a sale link for $999) for the same performance. AKA Bang for your buck. If you want a 6000W 'Clean' power honda - get ready to spend $3000. You can get a Kipor 6000W Clean sinemaster for $1500-1600. That is an absolute steal for something that could run a server farm.
Having said that - I would do the math to see how many Amps/Watts you actually need. A 30AMP/3000Watt unit has enough Juice to power an RV A/C unit.( and an FEC-100, a stereo, and a DVD/TV combo). Everything else is small in comparison in terms of initial power demand. Unless you need 50 AMP service, you shouldnt need anything so big. Maybe you do - if you do - and you need it to be clean power. go with the 6000W model.
I know you say noise isnt an issue- but the Clean Gensets also have great sound protection. far better than just adding a muffler addresses. They are enclosed, muffled, and engineered for quiet ops. You are looking at 58-62dB for a "Clean" gen set to 70+ db for the ones at Costco. I called BlackMax, Coleman, Honda, and Robins - and none could give me a rating. That is because they were over 72db. 58db you can talk over in a normal voice, standing next to the unit. 72db you can be yelling at each other and not hear it....
Good luck with whatever you choose to get. But if "Clean" power is your need, you won't get that at Costco.