FWIW, I have no experience with the 090; scrutinize my comments and make your own decision. But as a few general comments:
I like that you are using port maps. It is good to have a plan when doing a project, and IMO the best way to go about making a jug perform better.
The engineers aren't dummies. They can design these motors to do exactly what they want, though there are always compromises. What they do not have is much (any) oversight in quality control over modular components. Parts may even be built by different plants, maybe sometimes even different companies. The result is a motor, that once random parts are assembled, passes spec, but it not exactly what is on the drawing table. Alignments may be of a few thousandths here, casting flaws there, cutter marks, port mismatching, etc. etc. Point being, a basic blueprinting of the motor, simply getting the motor to its original spec, will make an significant difference in performance. Throw is an exhaust mod to correct for emissions standards, and you have a whole new baby.
That said, my conjecture is that your transfers are a bit aggressive. You've got a lot of experience, so you know it only takes small changes to make big differences. I think you are risking a loss of flow velocity (or at minimum, designed scavenging) by making such a drastic change. Ostensibly, it would be fine if you were trying to make a race saw, but you said you wanted it to stay in the 8500 RPM range. You can fill the combustion chamber with air using low volume and high velocity transfers or high volume and low velocity transfers. This saw is already turning low RPM, so increasing the volume of the paths the air is traveling, so drastically, at such low RPM, is potentially going to slow the velocity. Like said, if this were a 12-14K race saw, then the rules change. Metal is easy to take off, but a PITA to put back on
When it is all said and done, whether you are running 8500-9500 RPM, I think you'll notice the best performance gain in cutting by getting a much larger rim. That is, unless you do a lot of cutting of 5-6' trees, in which case I am very jealous