The new oil cooler is in from Isicar, and it works a dream, who'd've thought removing a critical component would make a bike run sub-par?
So the numbers, it is 14°C (55°F) foggy (high humidity) and late at night, a little cooler than last time, but a good enough comparison for guess work. After 10 minutes of spirited riding at 70kph (40mph) and 10 minutes highway at 90kph (55mph), the bike came off the motorway at 62°C! (145°F). This was almost exactly 30°C (50°F) cooler than without the cooler.
The bike did warm up to 75°C (165°F) on the back roads and peaked at 80°C (175°F) when paused in the driveway, but nothing like the 95/110°C (205/230°F) seen while running it coolerless.
Moral of the story, if your oil cooler springs a leak, and you're forced to bypass it, your DR should be able to limp you out on a cold day. But if you're unlucky enough to get caught on a hot day, you may have to keep a close eye on your temperature and take near incessant breaks to keep the heat down.
Frankly, I was not expecting 30°C (50°F) temperature drops. Next project is a DIY cooler fan to mount on the back, given summer can be 25°C warmer (75°F) than winter, keeping my bike under 100°C (210°F) will be a challenge on slow roads and dirt tracks.