500 mg of oral Vitamin C daily will generally achieve about 90% of serum levels possible via oral dosage. Increasing the dose to 1000mg will give 94-96% of possible serum levels. It is difficult for doses higher than that to raise levels any higher, although men may get a couple extra percent than women do.
For most people, 500 mg to 1000 mg daily is a sufficient dose, and if taking 1000 mg daily, better results might be achieved by dividing the dose to 500 mg twice a day.
Liposomal Vitamin C may give slightly higher serum levels than regular Vitamin C, but the levels are still in the micromolar range, while IV Vitamin C will achieve much higher levels.