Current mainnet gas limit per block is 8M (7.99), that of Ropsten is 9M (which is actually rather surprising as it was 4.7M two months ago and I did complain about it...).
Given the above, what's the recommended best-practice gas limit for a single transaction? Would 6M be too high and risk not being picked by the miners if I'm aiming for median gas price? How about 4.7M?
After all, is there any statistics on the distribution of the gas used by mainnet transactions?
Edit: It seems I've not made myself clear enough. I'm referring to the transaction from my contract function. The function does something iteratively, and it's up to me to decide how many iterations to process within one transaction. My question is basically trying to gauge the maximum amount of gas "safe" to use with a reasonable gas price.