Sorry for the delay in replying, but....
I've now done 1,500 miles in the Octavia - the classic mix of town, country and motorway.
Plusses:
The driver's area is plenty big enough for a six-foot me and there's been no complaints from my wife or 89 year old mother about accessing or legroom in the front passenger seat.
The boot may lack the Narnian dimensions of a Superb but it was plenty big enough for our holiday baggage.
The ride is firmer and a lot easier over speed humps.
The 2 litre diesel is about 15-20% more economical than the equivalent Superb.
It's £100 a month cheaper to lease.
Long distance driving is just as easy, or as similar as makes no matter.
Parking and city driving are a lot less stressful both for my co-pilot (she doesn't drive) and I. I feel like I'm in control of the car rather than the other way round.
Minuses:
A couple of things aren't as big as I'm used to - central console, rear view mirror, that sort of thing.
One or two bits of finish (especially the door handles) make you realise that the Superb now really is executive standard. There's a lot more clinking than solid thudding.
The infotainment centre is of the "It wasn't broke so why mend it?" variety that's taking me forever to understand. In particular I can't get rid of that bloody woman's voice forever asking what me what I want to do.
It doesn't look anywhere near as impressive as a Superb.
Overall: It's a nice car, it's a lot cheaper and it's probably at the same level now as my first 12-plate Superb. They're both, in their way, great cars to own & drive. You pays your money, you takes your choice.