In my view G1/J1 is primarily a Pacific strategy, and G1/J4 is primarily a Europe strategy.
If you are doing G1/J4 your goal is to take Moscow on G5. Â To do this you need to send everything east, and your builds are mech and armor on G1/G2 and mostly bombers on G3/G4. Â On G2 slingshot the German mech/armor from France to Slovakia with a strafe of Yugo. Â Start strategic bombing Moscow on G3. Â The effect of all of this is to put an overwhelming force in Russia and limit his ability to respond. Â The other effect is that western Europe is thinly held with just enough to beat back UK landings. Â You cannot afford to have the US show up in Europe before G5 when you take Moscow and more importantly drop a large land unit buy into western Europe. Â Having Japan wait until J4 means the US goes to Gibraltar on US4 and lands somewhere on US5 (after you have done your defensive build on G5). Â Japan spends it time beating up on China and Siberia (the Japanese player may feel a little frustrated because his fighting capability will be under utilized). Â On the other hand the psychological and economic effect of an earlier Moscow fall is hopefully worth it. Â If you release Japan early, the US will show up in Europe too soon and Germany will be forced to divert resources from Russia at the crucial moment and the move on Moscow will likely flounder.
In a G1/J1 I think the primary goal is to distract the US into sending an inordinate amount of resources to the Europe side, hopefully leaving Hawaii or Sydney vulnerable early. Â If this happens, then its a game winner because in a J1 taking Calcutta is usually a foregone conclusion. Â Even if the US does not skimp too much on the Pacific, the earlier presence of US help in Europe, will force Germany to slow its initial blitz of Russia to defend Europe. Â This is not necessarily a bad thing, it just means as Germany you are going to shift gears to a more standard and methodical approach to Russia.
Going G1/J2 just seems to give up the advantages of J1 and just gives the US a turn to get ready for war.
Going G1/J3 is like being half pregnant, you have lost the advantages of an earlier J1 or even J2, and the US will wreak havoc on Europe before Germany is ready. The only good thing is you would get the jump on an almost certain UK/ANZAC DOW on their turn 3, thus denying them a big haul of NO’s (but if you don’t like the prospect of a much stronger UK/ANZAC then you might as well do J1)