Picking up on some earlier posts. The "30,000-foot deadline" demanding pressurization for crew survival.
The European theater required the B-17s and B-24s to operate at high altitude to pass over hostile territory. Usual transit and over target altitude was on the order of 25,000 feet, with the crew on oxygen and wearing electrically heated garments. While range was not a major problem in ETO, a direct climb to altitude reduces range substantially.
In the Pacific theater, operating from isolated island bases and flying over long reaches of largely undefended ocean, there was no military reason for climbing to altitude immediately, even if the overheating R-3350s and high drag cowl flap position would permit it. Where it is necessary to maximize range, the aircraft must be flown at best L/D. This is obtained at the lift coefficient where drag is lowest and, correspondingly it can be held constant, at its optimal value, by controlling speed and air density as aircraft weight decreases with fuel burn. This can be accomplished by slowing down, by climbing to higher altitude where air density is lower, or a combination of the two. Combined with the sad operating characteristics of the CW R-3350, it appears that (I don't have any mission profiles in front of me-) B-29 missions out to the Empire would be flown in a gradual slow climb (or series of step climbs) as engine temperature permits, with cowl flaps being closed toward the in-trail position, and maybe even gradual power reduction as the ship burns lighter. I can't imagine that the entire mission would be flown at 30,000+ feet if range was in any way critical. It is possible that average B-29 mission altitude was actually lower than ETO.
Pressure cabins are great if there is no chance that they could be punctured and burst explosively. Did B-29s depressurize over target?
Considering temperature lapse rate in the standard atmosphere, aircrew at 30,000 in an unpressurized aircraft would be about 12 degrees F colder than at 25,000 feet. With full-flow masks available, breathing would nominal at either altitude.
I note , from USAF specs, that the B-32 service ceiling was all of 1,150 feet lower than the B-29, normal cruise was 20 MPH faster, and range figures, as presented, while not directly comparable, were in general similar. Since the B-32s empty weight was 14,250 pounds less than the B-29 (about 80%) for the same mission, the '32 might have been a better bargain.