@JohnCh@Croc you guys bring up good questions I need to ask myself. Most of them I already have comments on, but don't yet know my final decision.
For me, this car would be my fun car. Let me explain that a little bit. We have 2 children under 3 right now... my wife has an XC90 that'll be our family car. I have a 2019 STI that I bought new and has served me well as a family/dad car that I daily. I can do most things in it even with 2 kids, and am planning to keep that forever, and have it become a project whenever the engine blows.
The Caterham will be my daily with the STI, in the sense that, if I need more capacity, I will take the STI, otherwise, I'll always take the Caterham. I live in San Jose, and so weather isn't much of an issue. Maybe hot days will be unbearable in the Caterham though.
I'm not one to shy away from putting miles on a car, and so I'll take the Caterham to do kid pickup (once they're old enough), or groceries, or whatever errands.
I live 40 minutes away from Laguna Seca, so I ALSO want it to be my track car. Being a busy father has kept me from taking the STI even once, even though I've been itching to do so since I got the car... so take this statement with a grain of salt. I INTEND to go, might never make it.
@JohnChbrings up a good point in asking how visceral I want it. I got the STI over the M3 exactly for this reason. The M3 was too nice. I'm having a hard time deciding between the S vs R MOSTLY for transmission. The sequential sounds like it'll be great, but I do like to row my own gears, so I really don't know where to land on that one. I know that if I get the R, I will most definitely option the windscreen, doors, and roof, vs going that tiny carbon flap thingy (not sure what it's called). But I am also getting up there in age, so I'm not too sure about the light flywheel and the seats in particular.
The 420 will undoubtedly be enough car for me and my skills, but given that Caterham likely will be changing their lineup because of the UK ICE sales ban in 2030, and FOMO lol... should I get the 620 for "future-proofing"? It is a dream to get better at driving, and work my way up to a 620... so would I get a 620 now and work my way up, or get a 420 and trade up when I'm ready? Money is always a concern, but it's not a HUGE concern here.
I do drive barefoot/slippers a lot, so that statement about the heatsoak burning your feet is a little alarming.
I guess the big question is, will the 620 be too boring to drive around town, given how limiting you have to be with it? I'm a pretty reserved driver around town, and usually I don't even really rev out the STI. I get beat by Corollas and minivans ALL the time, so I wouldn't say that I'm afraid of driving more reservedly... but I also don't want a car that'll never leave 1st gear in town.