I think we're on the same page. Clearly v6 or v7 must be used to build for RPi, because those are the only two versions for which Linux/ARM support has been made available. As Kierkegaard said, existence precedes essence.
There were a couple community efforts to make a Linux/ARM build for v8, but try as I might I was never able to get a reply from the developer said to be working on it, so I have to assume those fell by the wayside.
Kevin has noted an interest in having an official release of RPi, but not likely before v10, and no offical commitments have been made so please let's not get all pitchforks and torches if other priorities push it further out.
Indeed, anyone with the intersection of skills, time, and interest could make a Linux/ARM build from the Git source. But alas that intersection has been difficult to find.
So until someone runs/debugs that make file we're using the object code for v6 and v7. Both are unsupported, so each is as good as the other, in their own way.
Yes, older software of any kind tends to outperform newer software. Rarely works the other way, esp. when Unicode happens in between. We've seen it with Python, and PHP, and others, and LiveCode is no exception.
And like the others, the version _after_ the first Unicode version start to get some of that speed back. While some things in v8 and v9 are still slower than in v6 (Unicode is demanding, as are the bug fixes which require more stringent type and bounds checking), but some things are faster.
So a "10x speed difference" is no doubt true in some cases, esp. when compared with the first Unicode edition, v7, I doubt it holds up across a sufficiently broad set of test cases, and am fairly certain it wouldn't hold up for v8 or v9 across a much greater range of cases.
But for RPi specifically, until someone runs that make file the speed gains and bug fixes in v8 and v9 won't matter, so pick either v6 or v7 as you like and enjoy.
As for this:
However, if your planning to use a newer IDE to create the stacks, how does that work out?
The simplest way is to use the version on your desktop that matches the engine you're running on the RPi. I keep v7 Community installed just for that purpose.
But if you really want to use a v9 IDE to make stacks to run with a v6 or v7 engine, no worries: the IDE has a way to save a stack file as any older format used for the last decade or so. Just Save As with the desired format and you should be good to go.