I hate to ask, but is there any chance of seeing some screenshot comparisons between the standard and maximum bitrate versions?

Maximum bitrate is well and good in theory, but as the pointless SuperBit series of DVDs proved, it doesn't always mean much.

Considering this is an upscale to start with, before a lot of artifact clean up, I can't help thinking that it doesn't really need a high rate to look pristine.

In cases like this, it's sometimes fun to do an OPV test to find what quantization value you get at the final target bitrate. (But I'm frequently crazy, have a weird idea of fun and I'm definitely not suggesting you actually do that.)