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That number is way out. Monero network is less secure then Bitcoin, but is also less worth so attacking it would bring less profit and is less likely to be attacked.
6 bitcoin confirmations is quite a bit. I think 4 are more then enough. One Monero block takes 2 minutes so in 40 minutes that Bitcoin should have 4 confirmations, Monero will have 20.
That number is way out. Monero network is less secure then Bitcoin, but is also less worth so attacking it would bring less profit and is less likely to be attacked.
6 bitcoin confirmations is quite a bit. I think 4 are more then enough. One Monero block takes 2 minutes so in 40 minutes that Bitcoin should have 4 confirmations, Monero will have 20.
Where are you getting this "4 are more then enough" idea? I guess that's true if you are buying a Frappuchino or Doritos. But "freshly-mined coins cannot be spent for 100 blocks."
Whoops, I screwed up editing and should have said "10 hours" not "6 hours" (assuming Monero's PoW is 10% as effective as Bitcoin's).
Yes, I know the number is "way out." It was merely illustrative approximation, as I cannot be arsed to look up and extrapolate from current actual figures.
The phrase "very generously assume" indicates Monero's PoW network strength is probably not even remotely close to 10% of Bitcoin's.
The actual figure is probably closer to 1%, so we're looking at 100 hours for XMR settlement security equivalent to 6 Bitcoin confs.
You and ArcticMine don't seem to be grokking the concept that 40 minutes of 100 megawatt XMR PoW is in no way equivalent to 40 minutes of 10 gigawatt BTC PoW.
That's basic high school physics.
Fixating on a side issue, that of direct economic incentives (cost/benefit) for attackers, is a distraction and spurious digression.
Speculating about motivations is in this context (answering astmandu's question about XMR settlement time) not helpful.
As smoothie pointed out, there exist infinitely more indirect incentives than the most naive possible direct monetary one.
The best example of indirect, non-monetary incentives is "I did it for the LULZ."
Regardless of our hypothetical adversary's incentive and motivation, attacking and orphaning 40 minutes worth of Bitcoin blocks would be roughly 100 times harder than doing the same to Monero. And that fact is reflected in their 100:1 market cap ratio.
So a good estimate of XMR settlement times must account for that vast (albeit rapidly shrinking) difference in the quality of the two coins' PoW.
The Work in Proof of Work is measured by the amount of electrical power consumed to produce a confirmation, not mere passage of time.
The biggest risk with the number of confirmations is not a 51% attack but natural chain reorganizations. This is depended on block time rather than the overall effective hash rate. The figures of 3-4 confirmations (Bitcoin) / 15 confirmations (Monero) are fairly typical in the industry.
For Bitcoin 0 confirmations is now a extremely high risk because there is a significant chance the transaction could be delayed for some time or even not mined at all. A simple "double spend" attack in this case is for the sender resend the transaction with a much higher fee, while the transaction is still unconfirmed.
Edit: Or simply send the transaction with a slightly sub optimal fee. Then there is a significant chance that the transaction is not mined at all, and there is no explicit "fraud" action of sending the second double spend transaction. This could make a criminal case for fraud very difficult if not impossible because of the need to prove intent. I suspect the current spam attack on the Bitcoin network is based on this premise. The spammer is counting on the fact that the vast majority of the spam transactions will never be mined.