Pitzury

I always thought the IR thermostat would be the best aftermarket choice out there and it is great you use this for your kit even though it is 3 times the price of the cheaper units. I bought my stuff over 16 years ago when there was a limited offer on the market. Now that i built my own 3 port thermostat I will use the Permacool for the power steering. Because I added a warm-up heat-exchanger to my system, I have to use 3 port thermostats. Otherwise the 4 port configuration thermostat is the easiest way to add an external cooler so the Improved Racing unit is the best choice available.
I am a big fan of Setrab but, 16years ago, Mocal was the only other option similar to Setrab. My setup now is a 625 core for transmission and 610 core for the power steering secured with 6 mm threaded rods and metal/rubber washers. A 9"in Spal fan cools both when needed. I used these because I had them already. On the Passat I use the 925 core with no fan. I believe the 920 and 925 cores work best on these cars and you are using the 920 core.
Nowadays SUSA has a great offer. As a matter fact I am thinking to get the remote filter from Setrab 18-RFHU13-22 because it can be rotated. Yeah, I added Magnom magnetic filtration, Wix remote filter, my own thermostat, one air/oil cooler, one water/oil heat-exchanger for warm-up and temperature control, a Magnefine in-line filter before returning to the transmission and all these with 8AN lines. Overkill or what? My car is street driven in ambient from -20 -+38*C with occasional towing. Slow speed and no AC was overheating the trans with the original tiny Copper tube cooler located in the cold end tank of the coolant radiator.

Ape Factory

I don't know what the flow rate is for the cooling circuit on the ZF transmission but you may be able to get away with the compact high flow unit (FSC) which is a bit less expensive. Shoot me a PM as I can get you killer deals on all the IR products as well as Setrab/Mocal.

The 625 is a solid unit but just not shaped right for the RS5/RS4/S5/S4 application. It has very low pressure drop and is large enough to handle the RS5's BTU output. I initially had that unit as a starting point but it just didn't work from a size/shape standpoint. For the S6 kit I'm working on, I actually use one of the IR cores which are fully welded construction and offer a lifetime warranty. They're a really great company and have been a pleasure to work with as has Setrab USA. The only issue with their cores is they come only in their raw finish. Can't get them in black.