I’ve always relied on mid-weight softshell trousers for my alpine climbing. I used to have a pair which I now replaced with these http://www.mountainhardwear.com/Men%27s-Warlow%E2%84%A2-Pant/OM4508,default,pd.html
Normally, I would wear trousers like these for summer climbing in the Alps, either mixed or pure rock. I made 2 trips to the Alps in the winter, and if it got really cold I simply wore a thick baselayer underneath. I never felt too cold wearing them, and the only times I wished I had something more waterproof were when being continuously rained on for 3 hours in Scotland, or while trying to half-sit down when taking a breather climbing easy angled snow (and getting my back wet). I suspect however that even the sturdiest goretex waterproofs wouldn’t help much in either situation?
The trousers that you mention owning are true softshell pants (no membrane) which are quite different to the membrane softshell pants which Jack and his mate wore on the N Face of the Eiger.
I bought some new true soft shell (no membrane) pants myself the other day. I think I'm going to get some 3/4 length Buffalo Teclite trousers made to wear under them when it's cold. I've used a similar combinations of trousers before, and found them okay down to about -15C.