I’ve ordered stocks from various makers over the years, but understand their CNC technology has improved to the point they now offer 99% fit.

Never ordered from Boyd’s, but have from Richards and from Great American Stock Co. My latest was from Richards and my choice required a fair amount of work since it was for a Siamese Mauser. I plan now to upgrade the stock on my Interarms MkX and would like to get some opinions on what to expect as far as fit and quality of wood. Not going with laminated, just a fancier walnut.

You makes your choice and spends your money and takes your chances.

No you ask me and I will tell you what you will get from them since I order stocks from both places frequently. Boyds are all CNC made and mostly drop in; fit is amazing for a factory stock. Richards; the top sellers are CNC made, the slow sellers, like your Siamese, are still pantographed. Not drop in, but very good; no gaps, but are not finished on the outside like Boyds; still need work.
GAG; long gone. and were pantographed like we all got for decades from Fajen and Bishop; in the dark ages.
So, there is no risk for your MK10.
Richards will have the best wood for the money; come over and I'll show you a few. And a dozen from Boyds.

Wenig.... they did really good for me...

I just finished up Richards stock for a CZ 23 Brno 98 Mauser the first stock was wrong on the end caps but they corrected it and reshipped the correct one, no hassle. Stock inlet was almost perfect very little work. The outside needed quite a bit of re-shaping to suit me but was good. Wood was better than I expected. All in all was worth the money in my opinion.

Wenig still uses the pantograph method and their pricing is much higher than Richards. ($245 for a plain walnut shotgun buttstock). I'll stick with them.

Richard's has improved in the last few years.

Yes, as I said, the better sellers, they now do with a CNC mill. The slower sellers, like Unc's Siamese, are still made on the pantograph, and are the same as they have been for decades. I used my first one in 1971.

i find it much better to find a nice blank and send it to onE of good duplicators

True, for the high end customs. These are for the average guy with more limited resources. Meaning, $.
You can get a nice looking stock for $300, which the average guy can inlet, and finish. From the wood sellers, you might be able to get a plain walnut blank for that price.

I would buy a blank and have a stylist turn my wood, that way I know my stylist and know my wood.I don't want 99% I prefer less as if the turned stock were to move get a nick, I could work around that if it was not too severe.