There's no single answer to this question, depends how much cash you have, how many points you have, how often you want to travel etc.. For my personal situation, I accumulate a fair number of points relatively easily/cheaply (and faster than I can use them), so I'd use points for airfare in just about every situation, unless I come across a mistake far or a dirt cheap domestic fair. However, if maybe I was a bit shy on points, I might choose to instead save them up for an international flight... rather than blow them on a $300 domestic ticket (for example).
In general 80K points a good value in terms of cpm for a $3K fare. However, this also comes down to valuation. For example, is that a $3K biz fare, where you could find a $500 econ fair... Or could you take a slightly different flight that might only be $1K. As an example, we're flying this fall from US-Italy RT for 63K Points (50K points in biz there, 20K points in ecom back, 10% rebate back), which is about a $2,500 ticket for that exact scenario. So am I getting 4.0 cpm? I say no... because there's no way I'd spend anywhere close to $2,500 on that ticket (I could actually fly econ both ways from an airport 2 hours away for $700 RT). Other people will say that yes - it's 4.0 cpm and you can get up to 10 cpm with Global First Class...
Not exactly an answer - but there is no one answer here.