The Defy 2015 SL will be more compliant - simply because the defuse design seat mast is designed to be able to rock back/forth. There'll be less 'defuse' action with the standard slide in seat post - thus the standard seat post will be less compliance. Although with the Defy 2015 advance they are carbon too so it's not too bad.

I really like the what the SL brings to the table but there's such a great fear in me in regards to being lock-down with the lack of adjustability of the ISP.

I'm using the ISM Adamo Attack - it's an amazing seat - the only one that's able to remove all my perineum pain. While I've got longer legs the Adamo is a taller seat so it will negate my longer legs advantage.

And now that the seat post height is so critical with an ISP - isn't determining the optimal seat post height a very protracted exercise - it's easier with the standard seat post where u can raise/lower the height. But with the ISP you pretty much need to be able to know the optimal seat height at cutting time.

Another question - are the little adjustments really enough for all the possible options the same rider will face? - shoes, pedal stack height - don't these sometimes can add up to quite a lot of height changes?

I don't see myself selling the bike in the near future - this would be THE bike for me (really!) - it's lightweight 7.4kg - has disc brakes and looks amazing. And being an average joe i hardly travel - if i do it'll be with the family, not with the bike.

Damn i want it so badly but I also don't want it to be a problem child.

Can I gather that everyone who's commented negatively so far about ISP has never owned an ISP bike?

The Defy 2015 SL 1 (ISP bike) weighs 7.4KG. The Advance Pro 1 (with standard seat post) weighs 7.9kg. So there's an increase of 0.5kg if i went with the standard seat post version.