So... I mined and never put any downward pressure on the exchanges. Quite the opposite, I removed (through evil hoarding) coins from circulation.
No. You didnt apply any preasure in either direction. Upward pressure is buying. Hoarding is pressure neutral.
To grasp the total "downward pressure" that miners put on the exchanges, one would have to know the financial situation and intentions of every Bitcoin miner, which is quite impossible.
The situation is different nowadays. Simple put there are 4 possibilities.
Miner buys with fiat and does not sell or spend coins. "Old case", since e.g. Ati didnt sell graphics cards for BTC. No coins are bought or sold on exchanges, pressure neutral.
Miner buys with BTC and does not sell or spend coins. Initial downward pressure on purchase since the manufacturers needs to sell BTC for fiat as the supply chain (e.g. chip manufactures) and staff get (at least mostly) paid in fiat.
Miner buys with fiat and sells coins on exchanges (or buys goods via services such a Bitpay). Delayed downward pressure since the BTC can only be mined after the hardware has been delivered.
Miner buys with BTC and sells coins on exchanges (or buys goods via services such a Bitpay). Both initial and delayed downward pressure.
As you can see there is not a single upward pressure case.
The "best" case for the BTC price from mining is neutral.
I dont know the percentages for each of those case, your guess is as good as mine. But mining obviously generates downwards pressure.
As opposed to a user of the currency. Probably not too many of those yet.
User buys coins and buys goods via e.g. Bitpay. Initial upwards pressure from buying, later downwards pressure from purchasing. Sum is pressure neutral.
And the last case, the speculator.
Speculator buys coins and does not spend them any time soon. Creates a direct upwards pressure on the price.
As price for BTC rises the downwards pressure from the miners increases (assuming the general composition does not change, that is the same percentage of miners still sell coins) and the upwards pressure from speculators decreases since the same amount of fiat invested will now buy less coins. And vice versa if the price for BTC drops.
And well, since your guess on the intentions of miners is probably as good as mine (10% of the miners selling? 30%? 50%? Maybe even 80% of total freshly mined coins?) you can directly calculate the required upward pressure required to keep the price merely stable. And dont forgot that a large amount of the mining pressure is delayed pressure, mining equipment worth three digit million dollars still waiting to be shipped ...