Moto bike for xc or xc bike for moto

Yes I have tried it quite a bit. Mx suspension doesn’t like roots or rocks very much. If you are fast it might be fine because you can float over some of that stuff at high speed. Ktm xc suspension is generally softer than Japanese xc suspension so a Japan xc bike might work better for mx and still be ok for xc racing. 

You’re into a revalve no matter what. Flywheels are cheap, tanks not to much. Pinch flats are a bummer on 19” wheels. 
 

I’ve always liked going the XC route and making the engine more peppy for tight single trail enduros, but would modify an SX in a heart beat if  I wasn’t living in 1st or 2nd gear riding 30” trail. 

I did this last year on YZ250x.......worked well except the goofy 250x gearing. If i was doing again i would have got the standard YZ. With Apex head - PV mod and FWW it was great woods bike and decent in MX. (gap from 3rd to 4th sucked)

Others will chime in - you'll be compromised in both places.

Used a yz250 for hare scramble races. Only off road mod was a 4 gallon clark gas tank. Moto suspension worked great and was ideal during rounds with softer dirt where deep bumps formed very similar to a rough mx track. As the other user said, suspension was not ideal at all when roots emerged from terrain. Roots and rocks were also rough with the 19 inch rear rim. I found the mx gearing to be a struggle in the woods sections and it seemed like I was always fighting between 2nd and 3rd whereas guys I was racing were more locked in 3rd. 

All in all I would choose the MX bike setup with a large tank over an XC set up unless I was doing a much tighter and lower speed style of racing (hard enduro or similar). 

I ride a yz250fx on track and trail and have no issues, bigger tank isnt noticeable on that bike and the gearing works

Kind of depends on the bike I would guess 

I used to race the Mideast series on my freestyle bike, and ride moto on it as well.  It beat me to death in the woods, but it made it just fine.
 

I’d recommend if you have the means to have a second set of suspension and switch between set-ups depending on what you’re riding.  I’d. Lean more towards setting up for harescrambles and XC, and stiffening it up for moto.  If you are only able to run one setup. Just adjust your spring rates to slightly stiffer than you need for woods and adjust clickers when switching between the two.  
 

Ultimately if you land where you’re supposed to, the XC setup is going to work fine for moto.  I just like the stiffer suspension in case you come up short on a bigger jump. Bikes nowadays are really good for a lot.  It’s been a while since I’ve raced in the woods, but I remember if I was trail riding with anyone slow I’d have the tendency to overheat on my moto bike (when I had two).  I’d say the answer to your question really depends on what you do more vs. what you can compromise on.  

I race a yz 250f Moto and off road/ hare scrambles (not extreme enduro) and it works great for me.  Suspension has been revalved and I have an fmf q pipe, can stiffen back up for Moto but I mostly prefer the enduro set up for all types of riding.  Have a Te 250 as well but I really don’t like It for racing mx on, just feels off, but great for more technical enduro.  Yz works well everywhere even beach racing. 

YZ450FX has been the best all rounder I've ever ridden. It'll pound dessert sand whoops, west Virginia single track, and motocross without me changing anything other than clickers. Majority of people would be better off with cross country bikes than pure moto.

Like others have said there will always be a compromise. I rode my stock 2019 KTM 350 SX-F in several harescramble races. I lowered the air pressure and softened the clickers and overall it was good. Not great, but definitely rideable. I have a XC setup now and it tracks better and is overall a more enjoyable setting compared to the stock moto setup. I honestly like the XC setup I have on the moto track as well. The only issue I have is when a track has tight whoops or doubles and the suspension just doesn’t have enough dampening for the feel I like.

It’s sounds like you use moto as a training device for woods racing, so if it were me I’d rather have woods suspension for racing.  

If you're racing NYOA scrambles their courses are fast and not that technical imo, you could get away with a MX setup but getting the suspension setup for a more GP style setup would probably be the ticket.

I only really have experience with the yz250f and fx, but the stock FX suspension was perfect for GP for me and too stiff for rocky scrambles/enduro. I also train on the moto track and just accept my woods setup will bottom pretty often; I would lose more time in the woods than I would gain on the track by going to a stiffer setup. I think the biggest difference between the MX and XC models are the gear spacing, everything else can be changed.

To me it sounds like a no brainer if you just use moto for training but race hare scrambles (that's what I do as well). I've never had any issues moto'ing my 250. 350, and now 300xc. I recently picked up a beta 200 race edition but that will not be seeing a moto track without a revalve lol