I tried a Sigma 30mm f1.4 & it was disappointing enough for me to return it but I gather the Sigma quality is variable so you might be able to get a good one.
I bought an FA 31mm f1.8 Ltd. & it also is disappointing wide open but it's a lovely lens apart from that.

It does indeed have iso 100 but not if you use the expanded dynamic range function which I habitually use on my K-7 because it's DR is disappointing.
Pity they pulled the article as I would have liked to read it.

One thing I forgot:-
greater dynamic range. I habitually run my K-7 on the max. dynamic range setting which means I have to use a min. iso of 200.

The K-7 images are softer than the *istD - hence less detail.
Sure I haven't tested them side by side but was my initial & continuing reaction is the K-7 is softer.
I'm only telling you my experience without any axe to grind. I'm always sceptical of reviews as you rarely hear the bad news until the new improved model comes out. I gather the Canon 50D is a case in point.

I'm not viewing at 100%.
Prints of photos taken by the *istD look sharper than those taken with the K-7. They also look sharper on my monitor at normal resolution (where I can see the entire image on the screen) which is one of the disappointing aspects of my K-7. The Samsung sensor is not a great one & it's noise performance is poor (also worse than the *istD which is understandable given the extra pixels crammed on the sensor). Which reminds me I must talk to my camera club mate about noise on his 18Mp Canon 7D.

As a K-7 user I would like:-
1/ a larger, brighter viewfinder
2/ better sensor; not necessarily more pixels but more detail. I haven't tested them side by side but I feel for detail my old 6Mp *istD at least equals if not betters my K-7
3/ faster processing
4/ more accurate focus
5/ better high iso (800+) noise performance

I passed up the one in the US as too expensive but bid AU$1021 on the Oz one but was beaten by $1042. Could have gone more but felt for a second hand lens that was enough when I can get a new (silver - which I would prefer) one for $1342 in Oz.

My first was a Spotmatic & because I wanted to shoot both colour & B&W I subsequently bought an SP1000 like yours. They were both great cameras, hard to kill & reliable. The SP1000 had a better arrangement for loading the film end into the spool. Who cared if the light meter battery was flat just guess the exposure & keep shooting. how different it is today.
Looks as if we cut our SLR teeth about the same time John.
Regards, Ian.

That was *one* FA31 @ $1000 - it will be interesting to see what the couple I'm watching make.
Regards, Ian.

Thanks Bob. I let one get away on ebay recently without bidding on it though it did make rather a lot of money - $AU670 & I've seen an FA31 go for not much more at $AU1000.
Regards, Ian.