Suggestions on new fans and heatsink

I have a Fractal R4 with a side window. I was thinking about upgrading the fans to noctuas in the front to maybe get better flow and more positive pressure in the case. The current fans are pretty quiet and I use the built in controller on the front to keep them powered down. My tower sits about a foot from me on my desk so I'm pretty aware of any noise in it and I'd like it as quiet as possible while still giving good cooling. Would the noctuas be a worthwhile upgrade over the Define stock fans since the cost is so much higher? I have both front fans and the rear exhaust populated and the top HDD cage removed for better flow. I'd also like to upgrade my CPU cooler to one that would be quieter as that is the loudest thing in my case right now, I run a hyper n520 that has 2 90MM fans in push/pull I'd like to upgrade to something that might give better cooling but would be much quieter possibly a noctua cooler as well?

The noctua nh d14 is pretty much the best air cooler around. I have one and its almost inaudible with the low noise adapters. I don't have an r4, so I can't comment on the noise of the stock fans,  but I would assume that noctua fans are probably gonna be a good upgrade. Alternative coolers would be the xigmatek dark knight or the phanteks heatsink.

If you would like a cheaper solution the enermax twister blade fans that are on this one are really quite on a budget and with the pwm control you can set the speed in your bios

Thank you for both of your inputs. I've been wanting to try the noctua but it's hard to justify the price without ever having tried them or seen them in person. My only concern with the D14 is that it may conflict with my high profile ram so I've been looking into the NH-U14S because it's a little thinner. The Enermax doesn't look like a bad budget solution though and its reviews were great I'll definitely look into it as well.