Image Credit: Kith.The first-generation BMW X5 never received a full-fat M version, leaving enthusiasts to wonder what might have happened if BMW's performance division had been given free rein. More than two decades later, Kith founder Ronnie Fieg has effectively commissioned an answer.His extensively rebuilt E53 X5 combines the naturally aspirated V10 from the E60-generation M5 with a six-speed manual transmission. Even better, the conversion retains the X5's factory all-wheel-drive system.The one-off was created as part of Kith's continuing relationship with BMW and made its public appearance during Monterey Car Week. Rather than producing an extravagant show car, the project follows an OEM+ philosophy intended to make the finished X5 look like something BMW itself could conceivably have built.AdvertisementAdvertisementThat approach makes the mechanical specification even more enticing. Underneath the relatively restrained Titanium Silver Metallic body lies one of BMW M's most memorable engines, three pedals, and the practicality of the SUV that helped define the modern performance crossover.An M5 V10 Finds A New HomeImage Credit: Kith.At the heart of the project is BMW's 5.0-liter S85 V10, the high-revving engine originally fitted to the E60 M5 and E63/E64 M6. In factory M5 specification, the naturally aspirated unit produced 500 hp and 383 lb-ft (520 Nm) of torque.For Fieg's X5, the engine was rebuilt by CarBahn with forged pistons rather than simply being transplanted straight from a donor car. The team also developed a custom exhaust system to suit its unusual new home.Perhaps the most interesting part is sitting immediately behind the engine. The V10 is connected to a six-speed manual gearbox, while the original X5 all-wheel-drive system has been retained.AdvertisementAdvertisementMaking those components cooperate required extensive custom engineering, including bespoke engine and transmission mounts, wiring, software and supporting hardware. According to Fieg, integrating the engine, manual gearbox, AWD system, and electronics so everything behaved cohesively was the real challenge of the project.It Looks Surprisingly FactoryImage Credit: Kith.The E53 was completely stripped and restored before being rebuilt and coated in Titanium Silver Metallic. Its exterior takes inspiration from BMW's wild X5 Le Mans prototype, although the finished product is considerably subtler than its mechanical specification might suggest.Changes include revised aerodynamic elements, a lower stance, and four exhaust outlets. The X5 rides on 20-inch BMW Style 87 wheels, while a KW-based sport suspension and upgraded BMW M brakes help prepare the chassis for the additional performance.That restraint carries into the cabin, where the familiar E53 architecture is still intact. Kith added custom upholstery, extensive leather trim, and its own detailing without dramatically changing the original interior design.AdvertisementAdvertisementThere is one giveaway sitting directly in front of the driver. Because no production E53 needed instrumentation for an engine like the S85, a bespoke gauge cluster was developed with a tachometer stretching to 9,000 rpm.The X5 M BMW Never BuiltThe project feels especially believable because the ingredients aren't separated by decades of BMW history. Production of the original X5 continued through 2006, the same model year in which the V10-powered E60 M5 arrived in the United States.BMW itself had already demonstrated how extreme the E53 platform could become with the one-off X5 Le Mans. That experimental machine famously used a V12 derived from the engine powering the McLaren F1, making Fieg's V10 creation seem almost tame by comparison.Production X5 buyers never received anything quite so outrageous. The later 4.8is topped the regular E53 range with a 4.8-liter V8 producing 355 hp, leaving a considerable gap between the quickest showroom X5 and BMW's experimental V12 monster.Sadly, You Can't Order OneImage Credit: Kith.Anyone reaching for their wallet is out of luck. This V10-powered X5 is a one-off, and there are no announced plans for BMW or Kith to offer additional examples or a conversion package.AdvertisementAdvertisementIt won't simply disappear into a collection, either. Fieg has indicated that he and his wife intend to use the X5 as a daily driver in New York, which should give that 500-hp V10 and six-speed manual plenty of opportunities to stretch their legs.The original X5 helped establish the blueprint for today's performance SUVs, yet this project imagines a considerably wilder path BMW could have taken. A naturally aspirated M V10, manual gearbox, and AWD stuffed into the compact proportions of an E53 sounds like a recipe that would be difficult for any BMW enthusiast to resist.Would you take this V10-powered E53 over a modern X5 M? Or should BMW have built something like this when the original X5 was still in production? Share your thoughts in the comments.If you want more stories like this, follow Guessing Headlights on Yahoo so you don't miss what's coming next.