down - email Brian at dccontrollers and ask him your question - he'll give you an idea of what the answer is for your particular application. It's gonna vary with each application - the variable is how much of the fan's capacity will be needed to cool your car (auto or manual? a/c or no? Hot climate or no? Stop and go traffic or no?; other big electrical accessories or no?; extra cooling capacity in your radiator or no?) - you can see there are LOTS of variables. My SPAL fans pull somewhere around 30-35A at full speed. I have a/c and live in a fairly warm/humid summer southern climate. When they were operating in full on-full off mode, I didn't even try with the stock 65A alternator. I upgraded to a 95A unit. It was taxed when the fans would "hit". My voltmeter would stay pegged a bit above 14V under normal operating conditions - but when the fans hit - it'd drop down into the 12.5-13V range - which probably meant I wasn't charging the battery much. The idle speed would take a hit for a second til the computer could re-stabilize it.
Since I put the Delta Current controller on, the voltmeter almost NEVER goes below about 13.5V - and that's only at night with the a/c, lights and stereo on. In daylight driving, or with no a/c on - the gauge just stays pegged right up against the 14V mark. So it definitely made a HUGE difference in how hard my fans are working my alternator and battery. I got Brian's indicator light because quite frankly, I couldn't tell when the fans were on or off 99% of the time - with the controller there's no longer any indication like fan noise, idle speed variation or voltmeter drop.
The wild card here is how different is your set up than mine, and how 'hard' will your car need to use the MkVIII. Brian can help you answer that better than me. However, to me it's a no brainer. Because it controls temp so much more effectively, because it uses (most of the time) so much less current, because it's so much easier on the charging system and fan motor - it's worth it to get it for that alone. Put it on - if you find you have to upgrade the alternator anyway you haven't lost anything because - well, you certainly would've had to upgrade if you were running the MkVIII wide open with switches and relays.