Ideal lowered ride height

I swapped a set of BC Coilovers onto my car. We are preparing to do the final height adjustment and alignment. I had read somewhere that you should not go more than 40mm lower than stock, as it will cause problems with other components on the car (gearbox and steering bits). Sorry if this has been answered a million times. After trying several searches, I cannot seem to come across that info again (maybe I am using the wrong keywords). I want it to look good, but handling and functionality are the main focus. I got the standard spring rates with the BC setup (6k/4k I think), which seem to be fine for daily use, as the roads are decent around here. Is there a height that I should shoot for as ideal? Should I stick to the 40mm bit? That is about where it is sitting now, and I would not mind it being a little lower from an aesthetic perspective, but only if it will not cause any detriment to anything else.

I am running 15x6.5 ET 35 wheels with 195/50-15 tires if that matters. Should not have any clearance issues.

40 is all I would go if roads etc you use no issue for lower clearance . BC stroke is short so clearance generally achievable but that and practicality will be the controlling factors in final lowering figure .

Is there no concern for the angle that it creates with the steering bits and axles? That was my main concern. I do not want to cause any longevity issues in those parts. Do you think it important to keep the rear 10mm higher than the front, like stock (assuming stock figures I have seen are accurate)?

No concern at 40mm for driveshaft or rack angles. Good alignment and camber bolts on rear a must . I always front and rear same, sure some people level them .

Thanks for the info. The guy setting it up is very experienced in setting up suspensions, but just not familiar with these cars (he is a Porsche guy). I may look at another 10mm or so if he thinks the geometry on everything underneath looks good still. The BC setup has camber plates in the front, but I did not get anything for the rear. He was able to get it in spec where it is sitting right now (approx. 40 mm lower than it was with the worn out stock suspension).