You ask for a lot of comparisons here that require information that I don't think anyone on this forum can provide - What higher density layout for a voyager? Can you remove some of the accessible bogs, or not? I suspect removing crumple zones won't be possible.
I've heard some suggestions that the UK FLIRT design is mostly suited for 125mph, though I don't know how much work mostly is doing in that sentence!
I think, using the best information available, it is fair to say that a 125mph FLIRT is likely similar in density to an 80x
My source for seating numbers was wikipedia for the class 22x and 80x, which seems to have maintained its reputation for being wrong. For the FLIRTs I used the stadler-provided datasheets. That does explain the point noted by
@Krokodil, which surprised me as well. I've provided an updated table below with your seat numbers for class 221:
Class | seats | length | seats m^-1 |
Class 220 | 200 | 93 metres | 2.15 |
Class 221 (5-car) | 262 (XC) 256 (avanti) | 119 metres | 2.20 (XC) 2.15 (Avanti) |
Class 800 (bimode, 5-car) | 302 (LNER) 326 (GWR) | 130 metres | 2.32 (LNER) 2.51 (GWR) |
Clas 800 (bimode, 9-car) | 611 (LNER) 650 (GWR) | 234 metres | 2.61 (LNER) 2.78 (GWR) |
Class 745 (Electric only) | 704 (IC) 722 (StanEx) | 237 metres | 2.97 (IC) 3.05 (StanEx) |
Class 755 (bimode, 4-car) | 202 | 81 metres | 2.49 |
theoretical 12-car bimode FLIRT with 2 powerpacks | 704 (IC) 722 (StanEx) | 250 metres | 2.82 (IC) 2.89 (StanEx) |