"significant potential upside[s]"
With little time for Congress to pass more legislation before midterms, it's fairly unlikely that any additional stimulus measure will pass. Then, pretty much everyone expects Republicans to add to their seats in the House and Senate. Since they're born again deficit hawks, it's not likely that they'll allow more stimulus in 2011. So even though extending the tax cuts to the rich might not be the best form of stimulus, it might be Washington's only option.