Las Cruces and Portales, New Mexico are closest in altitude to Kampala, just under 4000 ft. The NCAA altitude conversion for them for the steeple is about 9 seconds. So, Cheptegei's time trial would have been worth about 7:32-33, very fast. Monaco weather's usually a bit warm for the 5, but perfect for the 1500m. Try for the world record at a cooler meeting, maybe in Switzerland, if this doesn't work.
Top Ten all-time:
1 12:37.35 Kenenisa Bekele ETH 13.06.82 1 Hengelo 31.05.2004
2 12:39.36 Haile Gebrselassie ETH 18.04.73 1 Helsinki 13.06.1998
3 12:39.74 Daniel Komen KEN 17.05.76 1 Bruxelles 22.08.1997
4 12:40.18 Kenenisa Bekele ETH 13.06.82 1 Saint-Denis 01.07.2005
5 12:41.86 Haile Gebrselassie ETH 18.04.73 1 Zürich 13.08.1997
6 12:43.02 Selemon Barega ETH 20.01.00 1 Bruxelles 31.08.2018
7 12:44.39 Haile Gebrselassie ETH 18.04.73 1 Zürich 16.08.1995
8 12:44.90 Daniel Komen KEN 17.05.76 2 Zürich 13.08.1997
9 12:45.09 Daniel Komen KEN 17.05.76 1 Zürich 14.08.1996
10 12:45.82 Hagos Gebrhiwet ETH 11.05.94 2 Bruxelles 31.08.2018
The top ten all-time were all run in cooler places, Belgium, Netherlands, and Switzerland, except for Bekele's run in Paris (St.-Denis). (It's 93 degrees today in Hengelo!) I wasn't able to find the weather in Hengelo in 2004 for the world record, but for what it's worth in May 2010 it was in the 50s and low 60s.