there's a reason trangs set is used for FRW setups. Besides being a quite good amount of overall damage- 3 piece trangs being already optimal and the armor & full set bonus being good- the vampire form has a significant boost to base run/walk speed that greatly increases how fast you go. All normal human player models in d2 have a base run/walk speed of 9/6 yards per second. With trangs, you have 9/9 base. Since overall run/walk speed is calculated as
total = base_run_or_walk + (%frw * walk speed)
trangs allows you not only to walk at the same speed of running and have +3 yard/s walk speed and keep your blocking & defense since you're walking, but also increases the effects of %frw

with 178% frw, a trangs build walks at 16.29 yards/s and can keep its 75% block and defense. With the same frw, a non-trangs build runs at 13.86 with 25% block and no defense, or walks at 10.86 with block/defense.