Hi Ernie
I have been running a 9110 here in the UK since May and have put fair amount of 400 gsm through it, here are my experience.
One of the first jobs I ran was on Conqueror 400 HWW. There was a small amount of shrink along its length on both sides but once this was compensated for backed up fine, with around 0.25mm of movement back and forth during the 2000 sheets run with no jams or mis-feeds.
A couple of weeks back I ran 500 double sided Conqueror 400 Laid which had to be hot foiled on one of our Heidleberg letterpresses. The operator said to me that he was surprised how good and consistent the registration was.
Splendorgel 400 EW. This is an Indigo stock, we have two 5500's. it behaves a little strange due to the high fuser pressure and temp. The first side i get a small amount of image stretch and on the second side a small amount of shrinkage along the length of the paper but once adjusted for in the advanced paper settings it stays rock solid with hardly any movement back to front.
The last 400 gsm paper I have run in any quantity is Essential 400 silk 320x650mm. This stock is pushing the envelope of the machine spec and for this reason poses a few issues. You get a lot of shrinkage along the paper length which can be adjusted for but the main issue is side one, side two skew which is around 2 to 2.5mm. The leading edge ticks marks are bang on but it drifts out towards the trailing edge. If you balance it it means the 2nd side is 1mm low at the leading edge and 1mm high at the trailing edge. Once set up you get very little movement. Most of the jobs run on this stock are creased and folded to become A4 6pp so depending on the image its commercially okay. We have had no complaints. Although I have run some landscape FST covers which had an image which spread on to the 250gsm inners this was a bit of a challenge.
I have run a few other 400 gsm stocks not in any quantity, most of these are litho stocks such as EBB's Vision Superior which behaves very much the same as the Conquerors.
Hope this helps.
hojoclan