Before I mentally justify an upgrade can this make a difference...
Not that keen on 12m in the surf but sometimes 12knts is all I'm gett'n.
Current light wind kit is a 35ltr surfboard and a 12m airush flow (2009) on 26m lines. Kite has good bottom end but is slow even on its highest rear line knots. If the extensions were removed and the line length was 20m would it increase the turn speed proportionally to less power? Is it that simple?
Or have 2012 designs solved my needs and a reo or noise is calling.

Hi, most kites up to 3 years old are good.

I think different designs in the last 3 years have been more along the line of refinement and riding style plus guys developing a comfort for specific kites.

I am prepared to go for a faster moving/responsive kite on shorter lines than slow kite on long lines and if necessary a change in board to compensate any drop in bottom end

26 m are quite long lines. try removing the extensions, can't hurt and it's free.

I've got 23 and 25 m sets, and i notice the difference. 23m is faster. I don't notice much of a power drop, though I've no doubt it's there.

Not a lot of fat wingtip area there for turning leverage. So not a lot of 'tweaking' can be done.

Ok so that makes sense wing tip width (aka C Kite) = pivot turn speed. Reo's, RPM's, Noise's, etc.
But isn't the Bandit described as a fast turning kite and its wing tips aren't wide?
My kite design understanding seems to have a long way to go.

Theyre all described differently for marketing purposes....

I am yet to see a "100% depower" kite....

some get prett close but its all marketing.

I may suggest too that your turning speed will increase with an increase in wind speed. 12kts would turn your 12m into a fat cow in the sky....

and yes, it is correct that larger wing tips will provide faster turning speeds if tuned correctly.

But it does sound like a good excuse to put to the other half as justification for an upgrade...

First lesson in kitesurfing...
Dont ask the other half!!!