Ive used both of these in various office builds over the last few years and they are both solid choices for reliability. Between the two, I've found the Corsair RM750x 750W 80+ Gold to be slightly more versatile for a small room. While the be quiet! Straight Power 11 750W Gold has an excellent fan, the zero RPM mode on the Corsair means zero noise for the majority of your design work. In a small room that echoes, no movement is always better than slow movement. Budget-wise, you might want to consider the Seasonic FOCUS GX-750 750W 80+ Gold too. It is often cheaper than the be quiet! model and has a hybrid fan mode that works exceptionally well. I have been very happy with the Seasonic units in my workstation setups; they have a reputation for long-term safety and stability which is what matters when your livelihood depends on the machine. A few technical points to keep in mind for your quiet build:

• Zero RPM modes rely on internal heat sinks so ensure your case has decent passive airflow.
• Fluid Dynamic Bearings are essential if the fan does spin up to avoid clicking or grinding.
• 80 Plus Gold efficiency reduces heat waste, which keeps the fan off longer during your 9 to 5 tasks. I have used the Corsair unit for about two years now in a similar small office and have zero complaints. It stays silent until I start heavy rendering. Honestly, grabbing the Corsair RM750x 750W 80+ Gold when it is on sale is the smart move... it gives you high-end performance without overspending that $150 budget.

Just caught this and i love the dedication to a silent workspace! Real quick tho, what kind of GPU are you pairing with this for your design work? I need to know the total power draw to ensure you arent hitting the fan curve too hard during renders.

• Aim for a unit with Cybenetics A+ noise ratings.
• Grab Fractal Design Ion+ 2 Platinum 760W for amazing ripple suppression and safety. Better efficiency means less heat and way less noise!

Dude, I totally get the obsession with silence, I've spent way too much time looking at decibel charts lately! Zero RPM is definitely better than a slow fan for a tiny room because even a low hum can be super annoying when it echoes. I actually prefer the Seasonic FOCUS PX-750 750W 80+ Platinum over both your options because it stays in fanless mode even longer due to the higher efficiency. It is amazing! Here is why I love it:

• Platinum efficiency means way less waste heat to exhaust.
• Physical toggle for the hybrid fan control is super handy for testing.
• Compact 140mm depth makes cable management easier in small rigs. It usually sits right around $145 which is perfect for your budget tho. If you gotta buy by tomorrow, Seasonic is just the gold standard for silence imo. You wont regret it!