Originally Posted by SF Pauillac
$2.49/202.49m = 1.23 cpm. If you're doing this with Starwood, and end up converting the points to airline miles with the 25% bonus for the 20k transfer, it works out to 0.98 cents per airline mile, which is pretty good. I personally value Starpoints at more than 1.25 air miles, so I'd keep them with SPG.
If you also figure that you can invest that money for an extra 45 days or so (billing cycle plus grace period), say you can get 4% net of taxes (not too hard nowadays), that's 0.5% over the 45 days, which would make the cost in the equation above $1.99 instead of $2.49 (so 0.98 cpp and 0.79 cpm).
I did the Starwood AmEx deal, as well as the UA Visa one. But I believe the former was capped at a total $5K payment, while there was no cap on the latter. Also, IIRC, the former was only good for 4/15/06 payments to the IRS(2005 fed taxes), whereas the latter is there for tax payments of various sort through 12/31/06. So the Starwood deal was a good one, but couldn't get that much of it and no EQM possibilities in it.
Others give Starpoints a somewhat higher relative value to them over air miles, which themselves vary in value depending on the particular carrier, and it should be noted that Starpoints don't convert at that same favorable rate to all carriers equally (UA).
45 days from charge to payment due date is about the very best that one can do, and all the stars must be alignment to get that much "free" time (i.e., date when tax payment due, date when statement cuts, and grace period for credit card payment). I'm not sure what highly liquid investments presently yield 4% after all taxes (>6 or 7% pre-tax?), but not impossible.