It's a good question and to be honest - it's hard to say! I did the fans at the same time as I did the engine rebuild so I haven't got a direct comparison on a fresh engine. They are the same size as the stock fans (11"); you might just be able to squeeze in 12" if you wanted to go bigger.
Currently my engine temp sits at about 100 C in slow moving traffic in this weather which is OK I think. To be honest I thought it would be a little bit better than that what with the engine rebuild, but I don't know what would be considered low and high temps; however, I'm sure you'd get this with a stock fans as well. When I first got the car 10 years ago I am sure it ran fairly cool in traffic, around 90-100 (memory might be playing tricks there though!). I'm sure other people could confirm but 100 doesn't seem wildly low or beyond the realms of the OEM ones, but then who knows, if I had stuck with OEM fans I might be getting temps of 110 or so.
I did have issues with engine temps sitting in traffic for long periods in the couple of years before I started the rebuild, to the point where the engine would start to run badly, and be on the verge of cutting out. But that was with a tired old engine so not really a good comparison.
I also need to do an engine flush as I think deposits have built up in the rad (the old pipes I took off were coated) which won't help, so the fans might be battling against that.
For the moment I am a little bit sceptical about whether it was worth it: It was a bloody hassle to sort (although would be a lot easier now I've done it once and got a guide), it's not really that much lighter (if you were thinking of that - about 1kg less), and doesn't seem to be greatly cooler. Think they might be a little bit quieter.