Yeah, I know what you're saying. I did MX fork conversions with DR650s and inmates in the forum screeched and threw feces from the tree tops.
Comments in PMs like "A fork from a 250 can't possibly cope with the weight of a 650" gave me a reference point for assessing the knowledge of the contributor. Some people are clueless. I actually got abusive PMs for suggesting the swap could be done. I deleted the "how to" thread contents. If they want to be ungrateful they can go without.
At the end of the day, stock standard the MX forks work far better than revalved and resprung standard forks on something like the DR. Respringing them made them handle on the DR just like a 450 handles. They work exactly like they do on the smaller bikes. Quite literally you can ride the big bike just like a small bike. Over rocky fire trails average speeds according to my GPS went from 45kph to 60, then 70. Sections I had to pick my way through became sections where I point and twist. To the point where you have to start learning how to handle a large bike when in the air for extended periods.
I have a set of RM250 conventional dual chamber forks on one DR and I'd happily swap those onto the BMW. with a 0.55kg/mm spring rate and 300mm travel and 48mm legs they are far stronger, and far better at taking the abuse with the weight than the standard BMW forks. They were set up for a DR in full heavy touring set up with a 30 litre tank and gear. Heavier than a standard BMW.
I've actually given the idea a lot of thought. A motard disc on aftermarket wheel for an RMZ with a billet hub and super heavy spokes, fit the ABS ring, 4 Piston caliper. WooHoo. Every component is far stronger than the original BMW equivalent.
Properly built there's no reason at all I couldn't ride the F800 like I do my DR. It's a better balanced bike. Weight isn't the issue people think it is once the bike has suspension that is set up properly for the task. The DRs proved that to me.
The OD of the BMW steering head bearings is the same as the OD of almost every single Suzuki dirt bike steering head bearing from the last 20 years. The triples for the RM and DRZ conventionals are far stronger than the standard BMW ones.
It's a thought. Realistically, even the standard front end of a DR650 with Gold valves and heavy springs would be far superior to the BMW USD front end. Less travel than a pure off road MX front end, more travel than standard BMW, and a fork closer to the length of the standard BMW ones. Win/win. ABS sensor is easily set up on a DR front wheel.
Got a friend with a DR? Buy him an RMZ front end for $400 and swap. He'll love you for it.
Think outside the box.