As is the case with the offensive breakdown, the first set of numbers shall be the player's 2010 production, and the numbers in parentheses represent Bill James' 2011 projections. This comparison may be worthless, as I find it highly unlikely that the Yankees do not acquire another starting pitcher - but there is some value in comparing the top-four.
208 IP, 3.25 ERA, 3.13 FIP, 2.7 K/BB (204 IP, 3.53 ERA, 2.4 K/BB, 1.27 WHIP)
238 IP, 3.18 ERA, 3.54 FIP, 2.7 K/BB (236 IP, 3.32 ERA, 3.1 K/BB, 1.19 WHIP)
174 IP, 2.33 ERA, 3.61 FIP, 1.8 K/BB (193 IP, 3.54 ERA, 2.3 K/BB, 1.28 WHIP)
176 IP, 4.19 ERA, 4.25 FIP, 2.5 K/BB (177 IP, 3.56 ERA, 2.8 K/BB, 1.24 WHIP)
128 IP, 5.78 ERA, 4.54 FIP, 2.6 K/BB (168 IP, 3.86 ERA, 3.2 K/BB, 1.27 WHIP)
187 IP, 5.26 ERA, 4.83 FIP, 1.9 K/BB (191 IP, 4.01 ERA, 2.3 K/BB, 1.36 WHIP)
215 IP, 4.40 ERA, 3.85 FIP, 2.2 K/BB (227 IP, 3.89 ERA, 2.6 K/BB, 1.31 WHIP)
42 IP, 4.50 ERA, 4.36 FIP, 1.5 K/BB (80 IP, 4.61 ERA, 1.6 K/BB, 1.53 WHIP)
The first three match-up fairly evenly. Sabathia and Lester are bona fide aces. Buchholz may have a small edge on Hughes, but Hughes is less experienced and a couple of years younger. Beckett and Burnett have boom or bust potential, but I'd be comfortable with either in the middle of the rotation - Beckett's history is a bit better, but Burnett's been healthier over the last three years.
From there, the Red Sox take a tremendous advantage. Lackey was a bit of a disappointment last season, but he improved dramatically as the season wore on - he's a much, much better option than Ivan Nova. I'm not quite sure who the Red Sox will utilize as their fifth starter, as Matsuzaka and Wakefield have had their issues, but that flexibility is an advantage, as well. I would take either over Mitre at this juncture.
Again, the offseason is not over. The Yankees will not enter the season with Nova and Mitre, Brackman, Phelps, or another rookie at the back of the rotation. Even so, they would need a fair upgrade to match the Red Sox.