I strongly encourage that you maintain physical contact between the grounded discharge probe and the capacitor for at least a full minute, and longer if measurements indicate otherwise.
The estimates that the formulas you used are basically fine; however, there are a number of assumptions embedded in them. Most notably that the resistance will remain constant over the discharge period. The problem is that with real world components, particularly when you putting hundreds of watts of power through them they heat up. Resistance in components change with temperature.
It is better to be safe, and keep contact for at least a full minute.
BTW, the resistance through your body was likely MUCH higher then 50K, because the resistance between your body and earth ground is in series. And if you were wearing shoes, it should have been quite a bit higher. The latter is why standing in water and getting shocked is so much worse. You only have your bodies resistance to deal with at that point.