A fab basement at 42 °C with a long, restricted exhaust-air duct is air-limited, not engine-limited. Here the genset that wins is whichever one holds 2000 kW standby at your ambient and your external static pressure on the fan — a number that only appears when you ask for the derated rating, not the headline one. The decision: get both vendors to state output at your exact room conditions; if one set needs a bigger core or remote radiator to hold 2 MW there, that cost lands on the install, and it may flip the whole economics regardless of badge.

The QSK60's Modular Common Rail holds injection pressure independent of speed, helping the engine recover fuel during the dip; Cat's electronically governed 3516 chases the same target by its own path. If your single largest step is a 700 kW chiller compressor starting across-the-line, that one event — about 35% of rating in a step — is what you spec against, and it is well into the region where the step-acceptance table decides the machine. Ask for that table at your step size and ambient; buy the set that lands it inside its class limit with margin.

If the fab's set runs only NFPA 110 tests plus genuine outages — call it under 100 hours a year — every added emissions subsystem is one more thing to fail between the rare moments it matters. The decision: at low annual hours pick the simplest compliant emissions path for maximum availability; only when local air rules force aftertreatment do you accept the dosing/regen burden, and then you weight reliability of that subsystem heavily.

A fab planning a second and third 2 MW set within five years should pick the control ecosystem now and stay in it. Mixing PowerCommand and EMCP on one paralleled bus means two load-sharing philosophies and two spares inventories. The decision: let the paralleling roadmap, not the first unit's price, choose the brand — the real spend is commissioning hours and spare controller boards across the farm's life.