Based on the data provided, we can observe that the coin in question has had an average auction closing price of 309.85 euros in previous auctions. Additionally, its current condition is graded at 95 (EBC+).

Considering that the starting price in the upcoming auction is 350 euros and the estimated average closing price has been 309.85 euros, we can infer that the closing price is likely to be above this value. Given the high condition of the coin (95), it is reasonable to expect that the closing price will remain in a similar range or higher than the historical average.

Therefore, my estimate for the maximum purchase price for this coin in the next auction would be around 350-370 euros, considering the upward trend in previous closing prices and the outstanding condition of the coin.