Theres a NEW Dolan seta

74 deg head angle, 25mm tyres and 38mm rake gives the perfect 58mm trail

Tyre Clearance 23mm Max

You're right, thats fine. Not too twitchy but still agressive.

Why not?

How good would be for a superlight London commuter?
PS: I am aloud only one bike (space restrictions) and has to be a good one...

Well it hasn't got any mudguard mounts for a start

No 60cm :(

Dolan website states tyres 23mm Max, though it looks that would take 25mm...?

it looks that would take 25mm

I'm curious what makes you say this.

I can see pictures with the seatstay bridge is about 1cm from tyre with the rear wheel axle relevantly forward in the dropouts. If the rear wheel axle is moved backwards (chain cut with one link longer) then it should give more space for bigger tyres, check pictures link below:
http://www.pedalroom.com/bike/dolan-seta--28383
https://www.lfgss.com/conversations/230728/

I am aloud only one bike

So you have to keep quite about the other ones :-)

;)

Without seeing chainstay clearance it's difficult to know.
Might be tighter down there in order to make space for the crank/chainring.

Here are some pictures:
http://www.pedalroom.com/bike/dolan-seta--28383

Dolan website states tyres 23mm Max, though it looks that would take 25mm...?

What a manufacturer can claim and what will actually fit are two different things, as EN 14781 says this:

"4.10.2 Wheel/tyre assembly – clearance
Alignment of the wheel/tyre assembly in a bicycle shall allow not less than 4 mm clearance between the tyre or the rim and any frame or fork element or a mudguard and its attachment bolts. "

I'm 1,84 cm high with 87 cm of inseem. Could the size 58 be good for me or should I take the 56 of the seta?

I'd go 58

I'd go 56

56!

Given that you won't run out of seat post on the 56, the biggest difference will be the reach. I'd think you could make either work with the appropriate stem length (depending on how much of a T-Rex you are). The 56 should give you a slightly more aggressive position because of the shorter head tube.

Others may have other considerations?

Hadn't considered head tube length, but I went 58 because I'm 181cm with 5cm less inseam than @ShadeBoyy, and ride a 56 Pre Crusa at the track.
58 Seta effective top tube is only 8mm longer than my 56PC, but a more appropriate seat tube length for rider's inseam and height.
Long top tubes look goofy, but IMO a spacer stack on a frame that's too small looks worse.
Size might depend on rider's preferred/current head tube stack.

@Levitz @Lukas
Now I'm a riding a 57*56 frame with 110mm stem with 1cm of spacer, the headtube is 175mm

I'd prefer to slam the stem, that's the reason why I said the size 58

The new batch of seta shoulf have arrived by their new owners by now. Any feedback concerning the frames? Complaints? Problems? Nive things?

They're nice, very nice. Bit disappointed the fork is not full carbon, mind.
Maybe a tad flexy- but that makes it superb on the road- probably shite for track use.

So what was the mistake Dolan realised that OP mentions?