I remember vividly about 2 years ago when I did the cooling overhaul, having the OEM WP compared to the Stewart EMP WP. It's like comparing the real deal with a toy. The difference is amazing.
Beside the stainless steel construnction, and very high quality materials, there's an important detail people often overlook: the beefed up bearing, which is very important if you use the OEM fan. That fan is not light, and the OEM sized waterpumps of any brand have the same small bearing rated for how many years? Does not matter if it's composite or plastic. If the impeller holds up, the bearing will go. There have been many reported WP bearing failures. The fan is heavy. The OEM sized waterpumps will hold longer if you use electrical fan.
Looking for a DIY? Parts? Check this out, it might be your ticket
TMS underdrive pullies - Stewart WP - PSS9 - Beisan Vanos seals - Zimmerman cross-drilled & Akebono Euro - Deka 649 MF - 55w HID headlights - 35w HID foglights - Hualigan double din - ACS (rep) alu pedals - Euro central storage console - Breyton Magic Racing staggered wheels - M5 bumper - M5 steering wheel - Tint
Stable: e39 M54, e53 N62 & Tribby