The 4 kW G120X as the catalog opens it: FSB frame, 230 V supply, 18.1 A nominal, 23.7 A max, unfiltered, IP20. The P ending is the standard designation, and the option list is empty - every other 4 kW variant adds something to this drive.

What does the standard P line get you at 4 kW?

The designation the catalog opens on. When a specifier pulls the 4 kW G120X, the P line is the entry the comparison starts from - and for a station that needs none of the options, the starting point is also the finish. No panel because commissioning happens once through a PC, no DC terminals because the motor cable runs short, no filter because the site plan does not ask for one. The alternative F line carries the same hardware under a second designation; the P line is simply the one the standard procurement flow quotes first, and for the plain station it is the whole answer.

Is 4 kW the right step - or 3 kW?

The step from 3 kW to 4 kW buys about a quarter more running current: 18.1 A nominal against the 14.1 A of the 3YC18, with 23.7 A for peaks. A pump or fan that sits inside 14.1 A is well served by the smaller drive - it costs the same frame width either way, both are the 100 mm FSB, but the smaller current rating is the smaller spend. A station whose pump outgrew the 14.1 A line, or whose fan wall grew past what the 3 kW step carries, belongs here. The step up is a current decision: 14.1 A to 18.1 A, not a frame change.