Depends on the amount of lead you need.......
But around 30 lbs for warm water diving should be OK........
The wing needs to be able to float the full rig on the surface without you in it, so..........
-11 lbs for the full tank (XS-120 HP), -2 for the BC (this might be off, as I am not sure about the TransPac), -2 for the reg, and assume 10 lbs of lead for you, totals -25 lbs........30 lbs wing is OK........
Now you clip on a can light, a pony bottle and you use a little more lead, then the 30 lb wing will not be big enough.......
My travel rig as an AL BP/W and Oxy 18 lb wing......since rentals are typically AL 80 tanks......and I wanted the very smallest for travel.......
Hope this helps......M