4pin fan on RAMPS board - direct? The question is simple - I have a RAMPS 1.4 running Marlin 1.1.9 with the three MOSFETs being used (end, fan, bed), but I'd like to have a couple other Marlin-controlled fans. One of them would be a 4-pin, 6000RPM cooler I got from a dead graphics card. Seeing how it runs perfectly at 12V 350 mA if I keep the control pin disconnected (and ignore the sense pin too, of course), Could I connect 12V and GND directly to the PSU (or RAMPS 12V header) and the CONTROL pin to one of the pwm servo control pins like D11? Or do I need a resistor? 

I could add some info about the fan if needed, but it's a FirstD 4-pin, 12V 0.35A fan that can run up to 6000 RPM.
Yes, this should work.

According to this 4-pin fan specification, such fans use a 5V PWM signal.
You would have to make sure the PWM frequency on the pin you use satisfies that 21-28 kHz range specified in the document.

According to 3.3 and 3.4 in the document, you may not be able to turn the fan off completely when using the PWM input signal.