The monsoon is nice and it would help any of the noise the 655 generates by isolating the vibrations within the acrylic of the res, but it's hard to say...I've never messed with one, so I can't really say. The MCP35x is PWM capable and will speed up/slow down based on your temps as monitored from your motherboard...similar to your CPU fan. It's a nice feature that isn't offered on most other pumps.
There are other res/tops for the 655 and the 350/355/35x, so it's a matter of choice. Almost all the tops for the DDC pumps help in the flow and head pressure. The 35x is kind of a different beast as that top was designed specifically for the pump to perform how it does. It might not help/hurt by adding a top/res either, but I don't know if you'd see the same improvements a top has made for the 350/355's in the past.
Tops for the 655 help by allowing compression fittings, different port angles, and flow rate improvements along with head pressure increases.