I think it depends on the soldering method. Promatch has a unique way to solder the batts together without the heat ever touching the cells. Professionally assembled by them is a nice feature they include.
Stick packs have very thin tabs between the cells and are spot welded. Side by side packs have thick low resistance bars and hopefully are well soldered. I have tested a stick pack at 20 amps for average voltage. Then disassembled the pack and put it back together using Deans bars. When I retested the pack, the voltage gained .2 volts. As the amps go up this voltage loss increases. But remember, stick packs usually go in play cars and the voltage losses are not seen.