As a design, Jaguar's XJ is aging about as well as one could ever hope for. Its slipstream, uncluttered lines have been largely unaltered since 2009, yet it still looks remarkably fresh faced. Coventry's biggest sedan is getting old, though, and it's always good to keep up interest by introducing new variants -- especially when the class you compete in is a murderer's row of talented models such as the Audi A8, BMW 7 Series and Mercedes-Benz S-Class. First previewed at the Goodwood Festival of Speed in camouflaged form, the 2018 Jaguar XJR575 moves the needle in a number of ways. For starters, the supercharged 5.0-liter V8 engine now has 575 horsepower (up 25 from the standard XJR), as well as 517 pound-feet of torque (+15). That groundswell of power is enough to zap the aluminum-bodied four-door to 60 mph in just 4.2 seconds and bound all the way on to a top speed of 186 mph. For those keeping tabs, the 2017 XJR -- which this model replaces -- hits 60 in 4.4 and taps out at 174. An electronic active differential helps ensure all that power is properly deployed, especially in corners.These days, aging in-car electronics tend to give away a car's vintage more than what's under the hood, so Jaguar is doing its best to keep the XJ up to snuff with updates to its latest Jaguar InControl Touch Pro infotainment system, which is available featuring quad-core power, a 10-inch screen and built-in 4G Wi-Fi. I've sampled both InControl Touch Pro and the standard system, and while it's still not my favorite piece of dashboard hardware, it's worth paying whatever you have to for the newer architecture.The car's also lacking the latest safety gear, which also gives away its age. But the advanced driver-assist systems available include automatic emergency braking and park, blind-spot and lane-keep assist. There's also the "Driver Condition Monitoring" feature, which warns of driver inattention due to distraction or drowsiness using a facial-recognition camera. Additional visual changes to the Jaguar XJR575 include unique twin hood louvers, and an aero kit including a restyled front bumper, side sills and subtle trunk lid spoiler. Gloss-black 20-inch five-spokes shrouding red brake calipers and unique badging round out the exterior. Satin Corris Grey paint (pictured) is an XJR575 exclusive, as is Velocity Blue.Interior changes are rather limited, with highlights including quilted seats with contrast stitching and a set of XJR575-branded door sill plates.No word yet on XJR575 pricing, but today's 2017 Jaguar XJR starts at $118,000, so figure a slight chunk of change above that to secure one of these rear-wheel-drive heroes in your driveway. It's expected at dealers late in the fourth quarter of this year.