I actually owned an 8" SCT and a 6" refractor at the same time and I set them up side by side in my drive one night. The 6" on some things did out perform the SCT, but on the moon and globs the SCT spanked the refractor. Some things showed about the same. I thought Saturn was far better in the SCT too, but Jupiter was about the same to my eyes.
As for which 140 and 152 I was referring to, the 140 was a TEC and the 152 was a TAK - both triplets. I know we're talking about doublets here, but the comparison was about how much the additional aperture would help and I was told it was a minor difference and not enough to justify going to the bigger tube. Again, I didn't see for myself but was speaking to someone who had gone through the same exercise of deciding between a 140 and 152 and had looked through both scopes.
Having owned an SCT I like the suggestion of considering a 9.25. It will really show you a lot. I had a 6.3 reducer that I kept on mine all the time. I really regret selling it, but I was accumulating too much stuff and something needed to go. I now think I chose poorly in letting my SCT go.
I also owned and compared my C8 SCT to the Lunt 152mm refractor, and found the Lunt to be better on - well everything! This is because of the contrast difference. This refractor rode perfectly well on my CGEM II. I think f/8 ED doublet refractors are the best, if you are using them visually. If 5th Gin is wanting to look at Globular star clusters, Planetary nebulae and faint galaxies visually, then your recommendation of the C 9.25 is very good if he takes it to a dark sky site, but all of those objects will stink in his light polluted environment. If he wants to view open clusters, double stars, planets and the moon and wide field views, then the refractor will give sharper and wider views and we should not forget the fact that poor and mediocre seeing always favors the smaller aperture instrument.
I say that f/8 ED 6" doublets are the best, because the slightly longer focal length allows them to get very good color correction without needing the heavy triplet lens. You need a six inch refractor to be as light as possible, because otherwise it is too awkward for one person to comfortably mount. You are right about the value of aperture. Since 5th Gin wants to use his next purchase visually, I think the extra 10 mm will mean a lot. He will be able to see the colors in Jupiter more clearly in the six inch and the cones of the retina will have 15% more light to work with. The 150 mm f/8 will get him 240X on Mars with a nice comfortable 5 mm eyepiece at a 0.625 mm exit pupil. To reach the same magnification, the APM 140 will require a 4 mm eyepiece with a smaller exit pupil of 0.57 mm.