Go for this lens!! (oh, you allready do..very good)
It´s such a good lens I think it might even be the sharpest of my CV lenses (nokt.50/Ultron28/Skopar21)..you really cannot go wrong with it!
I bought a cheap small digital camera case for it (with an small attached case for batteries/cards) were the skopar securely rests (the battery case houses the VF) and it´s allways with me!
I used it in Istanbul even in interiors with ASA400 film and got very sharp slides back at 1/8 or 1/15 soo easy to handhold a 21 so f4 is of no concern for me. (to get vignetting free images sharp from edge to edge you need to stop down a little but even at 4 it´s sharp enough for me in the corners...center is allways perfect)
contrast is on the high side but I love the colour rendition i get from it.
heres some shots to prove my point ;-)
at f5,6 I love the detail straight to the corners (on TriX)
f8 or11 on Provia 400f after the rain:
f4 at 1/8th iirc .. the room was only lit by window light and the ceiling was dark(provia400f)
last one...also at f4 about 1/8 on Press 800 (but scan is from a print):
I hope this is helpfull (just in case you´r still undecided ;-)