First off, pack size is king, followed shortly by good magic mob rolls. Every map i run is first alted to this. Not only does it give more experience, but also way more map drops (it's like a MORE modifier for IIQ). Now that I've said that, here's a list of everything I do by map level.
Level 66-73: Just alt/aug for packsize/magic and run, easy to sustain and move up.
Level 74-75: Same as lower ones, except use 4 chisels on every map now. If I get an extremely good packsize roll (45%+) I may regal.
Level 76-78: Here's where it gets expensive. First, Chisel and alt for packsize/magic like before. Then I regal. If the regal is something I can't run like -max resists (does anyone run this in HC? Lol) then I scour and restart.
I then place it in the map device with 3 sacrifice fragments for 15% IIQ. I have constantly been buying them this league at 3:1c, and I feel 15 IIQ on a 76+ map with packsize/magic is def worth a 1c investment.
The last and final step is reserved only for 78 maps, and 77 maps that regal a second pack mod (for example alting to packsize, then regaling magic mobs). For these maps I have chosen to make the 8 chaos investment and add the "onslaught" zana mod to every single one. This gives 40% more IIQ which is huge. The final result is a 78 map with 35%+ packsize and 100%+ IIQ, which is equal to something like a 150% IIQ map without packsize. This is both amazing for experience AND map drops.
By using this system I have been able to maintain 77+ maps indefinitely. Plus, since I'm building up so many 76s (have about 70 now), If I ever run low because of a bad RNG streak I can always combine some of them for more 77s.
Now I'm sure the number 1 question will be, how the hell can you afford to add onslaught to every 78 map in a temp league? Well, in my experience, the onslaught mod helps sustain itself. It gives me tons of extra drops. This includes a large amount of level 71-75 maps, which I sell for 1-5c respectively. I also get a lot of extra currency, rare (Unid regal recipe!), and unique drops. All together this has allowed me to keep putting onslaught on maps.