i have fitted the Eibach Pro Kit springs + KONI Sport dampers. a great combo IMO, and had the same on my 156 TS years ago. ride comfort improved over the factory springs/dampers.
main issue is that with the V6, it does not drop the front...at all. well, not in my experience, and not from what others report too. but i think it does drop the front of a JTD a bit, though probably not the advertised 30mm, not sure. the JTD is 5~10mm higher than the V6 from the factory i believe, but also just as heavy in the nose. i suspect the reasons for the Eibach springs not lowering it are multiple, and include how low the front of the car sits alread (i never scraped the undertray before, but with some lowering it does, fairly easily), and the height of the front indicators/repeaters. in the UK, i think you guys have some regulations about the minimum height these must be off the road.
anyway, i had modified the fitment of the KONI's into the suspension arms, resulting in lowering of about 15mm. noticable differencene to the look (good), and the scraping underneath as mentioned!
plenty of people have the KW coilovers, especially v2 (variant 2). these seem a great setup for street cars, with the ability to lower till your heart's content, and very acceptable ride comfort. do a search.
if you can afford the KW setup, i'd go with that. if you are after a more serious setup, say for regular track work, then probably the Autodelta coilovers.
regardless, i still highly recommend the Eibach/KONI combo.