When I had my '58 International 3/4 ton 4X4, I went on the beaches in so. Calif/Huntington Bch. VERY soft/DEEP sand. The truck was a 6 cyl gas, 4-spd standard trans, 4. 10 differentials & I had 12 X 16. 5 X10-ply mud/snow tires.
I couldn't tell from your sig whether you have an auto or a stick. On the beach I let the tire pressure down to between 10-15 lbs. 1st gear was so low I never used it; I'd start off in 2nd gear. But, when the speed reached about 20 MPH and I tried to shift into 3rd, I couldn't shift fast enough. The truck would always sink into the soft sand during the shift and just "die... " So, I always stayed in 2nd gear on the beach, and top speed was limited to about 15-20 MPH.
However, on one occasion I happened to drive a new (about 1967 or 68) Chevy 4X4 pickup with a full-sized camper on the back; V-8, auto trans. We drove out on to the same beach -- without deflating the tires from hwy pressure -- where I had been limited to 20 MPH, and the Chevy with the automatic transmission accelerated smoothy up to around 40 MPH with NO hesitation.
If you have a standard trans, then low tire pressure is the key. If you have an automatic transmission, the tire pressure isn't so important.