Synthesizing "amendments for cloture votes" and 17 R's switch theories:
By the first theory, the switching R's include: Hutchison, Thune, Grassley, Coleman, Bond, and Ensign. That's 6.
We can be fairly confident that McConnell, Lott, Kyl, and Craig will switch. That's 4.
So we're up to 10.
And the 7 to get to 17 could include (from my vote list of "likely to switch"):

Collins (R-ME)--voted in favor of bill last year
Snowe (R-ME)--voted in favor of bill last year
Domenici (R-NM)--voted in favor of bill last year
Murkowski (R-AK)--voted in favor of bill last year
Stevens (R-AK)--voted in favor of bill last year
Smith (R-OR)--voted for bill last year, but could be up for a tough re-election...
Gregg (R-NH)--voted in favor of bill last year
Hatch (R-UT)--voted in favor of cloture last year
Bennett (R-UT)--voted in favor of bill last year

That's 9 in total. So are 2 of these 9 still on the fence? Was the Senate aide of the second theory lowballing the support for cloture? Can we rely on the amendments-for-cloture-votes theory?

Correction: Strike Cornyn; I don't know why I put him in this list; he doesn't have an amendment.