I just don't see the US sending a major army to CBI- one of the central premises of almost all US strategic planning against Japan was that a major land war against the Japanese, especially on the Asian mainland, would be a pointless waste of American lives for little strategic gain, and thus a major no-no.
In all the assorted Orange plans from about 1900 until they were superceded by the Rainbow plans in 1940-41, the Army & Marine Corps side of planning was limited to the defense of the Phillipines and other US territories, providing landing forces to capture whatever islands were deemed necessary to take, either to eliminate Japanese bases and establish US bases, and providing an army to retake/relieve the Phillipines depending on the circumstances. The main focus was always the naval offensive to neutralize Japanese bases, deliver the relief army to the Phillipines, eliminate the IJN as a threat, and if necessary, starve Japan into submission through blockade.
Considering that it really took the better part of a year to get a substantial, deployable field army into action OTL, if we assume that with a Japan-first focus, an army comprable to the US forces in Operation Torch can be deployed to the Pacific between July-September 1942 along with the associated air assets, what can these troops be used for? Assuming that this @ is roughly comprable to OTL, probably a bit more favorable to the Allies (not that much was sent to Europe for use by US forces before then, and although stocks of equipment were heavily used to resupply the British, and being to better equip PTO forces would have been really helpful, there's still only so many people to use them), it would seem that reinforcing New Guinea and Guadalcanal, and perhaps a more agressive tack in the Upper Solomons and subsequent campaigns would be appropriate, but still, not a major bump.
Although extra long-range bombers and fighters would be useful, the P-38 & P-47 didn't become operational in any significant numbers until mid-late 1942 and took longer to reach the front, and a PTO-focus might actually delay development of the Merlin-engined P-51 somewhat. The real bottleneck would, as has been said earlier, be naval strength. The naval assets in the ETO, a few battleships (a couple new, a couple really old), a couple carriers (Wasp goes to the Pacific a couple months earlier than OTL, which could have some effects, Ranger was considered to slow and fragile to be of any use in the PTO, and some CVEs of rather limited value in a fleet action), a few cruisers, and a bunch of destroyers probably aren't going to be enough to be strategic game-changers, so it will likely have to wait until mid-1943 for the necessary shipping to enter service. (Perhaps not building so many DEs and smaller ASW craft might speed that along a bit.)
So, unless as a result of butterflies from a pre-war POD that resulted in a PTO-first decision, there are significant trained & equipped reinforcments that can be deployed to key points such as the Phillipines, New Guinea, Australia, and the Upper Solomons right at the start of things, or prevent the blundering of MacArthur, Short, and Kimmel that led to US forces getting caught with their pants down on Dec. 7, a PTO-focus is going to result in Japan going down a bit harder, a few months earlier than usual. The real difference is in Europe, where the Soviets are going to be in a better position for the @ Cold War, because they'd likely end up with more of Europe to occupy and oppress for the next 50+ years of this TL.