I just boxed up my Ven-X (swapped to a NH-D14 this morning).
I honestly can't say I'd see how it would make a big difference due to the design of the Venomous-X and I find it hard to believe it would mount a 140mm fan comfortably regardless of what the specs say. You may actually end up finding it's more trouble than it's worth.
After typing the above paragraph, I did some quick research and came upon this:
YouTube - THERMALRIGHT VENOMOUS X 140MM FAN INSTALL