JR's 67% completion %, has yielded averages of 6.3 ypa / 9.4 ypc / 228 ypg.
CJB's 54% has yielded averages of 7.6 ypa / 14.0 ypc avg / 242 ypg.
-- (Numbers are skewed down by a much larger number of drops over a smaller number of attempts, at least 6 drops on CJB to 2 or 3 on JR.)
JR has commanded the offense to 20.6 ppg and a 2W - 1.5L record against #7 FCS defense, #56 and #103 FBS defenses.
CJB has commanded the offense to 27.3 ppg and a 1.5W - 0L record against #8 and #65 FBS defenses.
Not only have I watched them play, I've watched JR regress from his 4th qtr comeback vs Ball State to a very bad performance vs ISU and Pitt. Meanwhile, I've watched CJB work through the 1st half of Purdue and look very strong -- poised, precise and proficient -- as he settled in and the game progressed.
As others have stated, the ceiling is much higher with CJB and while you can cite completion %, I'll cite production and W's.