I should know this but while I had the 9" arm on my Scout and Scoutmaster and the 10.5" on my Classic there was a gap of several months between having them set up. Even though I am a dealer the exchange cost is not on the price sheet; I feel the 10.5 is the better arm but not knowing how much money is involved I am loath to give advice.
From what I recall, the JMW-9 to 10.5i upgrade is $1500 and the JMW-9 Signature to 10.5i upgrade is $1000. Prices may have changed and they don't seem to be listed any more on the VPI site.
I have a Superscout rim drive and changed from the 9 inch Valhalla to the 10.5i. I use the Benz Ebony LP in both. The difference was very slight indeed. The longer arm may even be a bit more fussy to handle, however, when you get used to it, it's as easy as any other arm.
I am with Stringreen, the difference is not that great; the 9" arm is very good. The Scoutmaster with standard arm is an excellent table; there was a gap of several months between the time I sold my demo and when I got the Classic in stock so I never directly compared them but as far as I can remember I liked the older table at least as well. Spend a moderate amount of money and replace the aluminum feet with solid brass ones. I am a Star Sound dealer so I used their Audio Points but any with a 1/4 20 thread will work. I liked the solid cones better than the Mini TNT feet but they are another possibility.
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