If you're after the same holy grail and have £270 spare I'd order a pair from sigma to check them out (before they disappear into "unknown delivery date" territory again, or pop over to me this week/end and get a feel for them and then order a pair.
They'll be put on my bike by this weekend and then taken out to Switzerland/Germany/France for a serious seeing to for a few weeks shortly after, so if you can hold out till beginning September I can give you a full road test breakdown.
If you're after the same holy grail and have £270 spare I'd order a pair from sigma to check them out (before they disappear into "unknown delivery date" territory again, or pop over to me this week/end and get a feel for them and then order a pair.