IIRC, the EU versions past 1.27 have a volume limitation (for the iriver fw obviously) due to some French legislation. For this reason I'd recommend using JP1.29 or similar. As an added bonus the asian versions allow for a wider fm band selection.
This is all just in case you ever want to use the stock firmware which now that you've discovered Rb you prob won't want/need to ever again!
As you are already aware don't us the US versions.
If you do opt for an asain version the language will default to that region's. To set it to english you will need to (from boot): Long press NAVI > First option (General) > Second option (language) > English.
Or the necessary button presses: Long NAVI > NAVI > down > NAVI > scroll to english > NAVI.