I dunno about Effexor helping with benzo w/d, but I'll tell you that getting OFF Effexor is very difficult. I tapered very, very slowly and still had the 'brain zaps', dizziness, etc. My brother was on it and was impatient to get off it, so tapered very little. He had zaps and other side-effects for months. There's a good reason that a lot of folks who've been on it call it Side-Effexor.
Best of luck - I recently got off opiates. Withdrawal can be grueling. Exercise helped immensely - with the anxiety, agitation, etc. and, I believe, helped get the natural endorphins and healthy hormones pumping again, much more quickly.
I also pumped up my diet with a lot of 'nutrient density' for nutritional support. Green smoothies, steamed veggies, salads, whole grains. It seems common to me that these two elements are under-valued as aids in withdrawal/recovery, but focusing on them helped/are helping me a great deal.