In reply to UKC Articles:
I have been to Peru five times and IME three weeks is sufficient time to do "2-3 5000ers and 1-2 6000ers." The secret is to choose a valley that has multiple peaks available while spending the minimum time traveling. The weather in July/August is usually excellent.
IMO The best spot for a quick trip is Quebrada (Valley) Ishinca. From the base camp at 4400m you have Urus Este (PD- 5420m) and Ishinca (traverse PD 5530m) as day climbs and Tocllaraju (AD to D on Normal 6032m) and Ranrapalca (NE Face D 6162m) as two day climbs with high camps. There is also the W Face of Tocllaraju at D that is a fine route on ice and snow and is an excellent introduction to harder routes on 6000m peaks.
If you add in a day each way between Lima and Huaraz, two full days acclimatisation in Huaraz, a day each way between the BC and Huaraz, and two days acclimatisation at BC doing walks, you have a total of eight days plus climbing time.
Very doable IMO, assuming that you acclimatise normally.