I currently have the JVC X7 I bought two years ago. Great picture and very nice black levels coming from an older Sony HD PJ. I know have the opportunity to grab either the X55R or a RS56U demo unit both under $3K here local in California.
The biggest question is will I see a major difference in updates such as contrast or black level performance coming from the X7? I dont watch 3D movies or play games. Movies only from my Oppo Blu-Ray player. Light controlled room.
Contrast ratio's vary between all three. Too hard to judge on that alone. I am still learning about the whole JVC PJ world. 4K upscaling is just a bonus.
For me the biggest change I would hope to gain would be black levels and sharpness if possible. That would be really nice.
If both are the same price, pick the RS56 as it has the better contrast. As to if you'll see a difference, maybe or maybe not, it depends on how well your room is setup. If you have all dark, non-reflective surfaces, then yes. There are other advances in 3D, light output, gamma, CMS, etc. on these newer pjs that will make a nice upgrade. If you do not go with one of them, mind PMing me the location of them?