the Atlas is basically too slow (48 km/h or so) to be useful in mechwarrior 5 imo
Okay, there's other reasons why it's not good and the speed isn't the problem, it's more the lack of guns. You are significantly better off with the Stalker STK-3F with 4 medium lasers, 4 SRM6s, and 2 PPCs, and the Banshee BNC-3S with 2 PPCs, 1 AC10/LBX10, and fill the rest with medium lasers though I don't remember how many because I don't remember the vanilla MW5 mechlab hardpoint limits for that variant because vanilla MW5 mechlab is pretty trash. There's only a very small handful of mechs that can out pace the STK-3F and BNC-3S, but all of them either come way too late to actually matter, or you can only get one of them per playthrough.
without a risk of overheating
This isn't MW3, or MW4 where there's degrading effects for being at higher heat and the possibility of shutting down before filling the heat bar, MW5 uses MWO's heat system which means the only heat point that matters is the very last one. Also because there's only like maybe a handful of actually threatening units in vanilla MW5, shutting down from overheating is nowhere near as bad as it is in MWO or even previous titles. Besides, heat doesn't matter if the other guy is dead, and all the harder encounters in MW5 (both in vanilla and the DLCs) are burst DPS races.
Okay, there's other reasons why it's not good and the speed isn't the problem, it's more the lack of guns. You are significantly better off with the Stalker STK-3F with 4 medium lasers, 4 SRM6s, and 2 PPCs, and the Banshee BNC-3S with 2 PPCs, 1 AC10/LBX10, and fill the rest with medium lasers though I don't remember how many because I don't remember the vanilla MW5 mechlab hardpoint limits for that variant because vanilla MW5 mechlab is pretty trash. There's only a very small handful of mechs that can out pace the STK-3F and BNC-3S, but all of them either come way too late to actually matter, or you can only get one of them per playthrough.
This isn't MW3, or MW4 where there's degrading effects for being at higher heat and the possibility of shutting down before filling the heat bar, MW5 uses MWO's heat system which means the only heat point that matters is the very last one. Also because there's only like maybe a handful of actually threatening units in vanilla MW5, shutting down from overheating is nowhere near as bad as it is in MWO or even previous titles. Besides, heat doesn't matter if the other guy is dead, and all the harder encounters in MW5 (both in vanilla and the DLCs) are burst DPS races.