We deal with this regularly, and using an over-the-counter (OTC) desk is definitely the way to go for large trades. It lets you lock in a fixed price without affecting the open market, which saves you from slippage and gets you better rates overall. We've been using Paybis for this, and their OTC service has been solidpersonalized support, secure transactions, and they handle everything smoothly from start to finish. If you're exploring options, Id recommend checking out their otc desk . Its made our big trades way less stressful.