I run the 52/42 osymetrics and I'm a devoted climber (125-130lbs). Most of the hills around me are short, around half a mile to a mile long and anything from 5% average to 14% average. I don't think I'd want anything less than the 11-29 I run at the back. To be fair when I'm really caning it I'll be down in the 25T sprocket but the 29 is very useful for when the gradient hits 13-25% or I just want to go a bit steadier on the hill.
The 42T ring at the front is 38T in the dead spot and 46T in the power phase, but this doesn't mean a great deal as once you get used to the chainrings, it just feels like a 42T round ring. Climbing with osymetrics are worth it, I feel like my pedal stroke is much smoother and more efficient - I always stay seated on climbs and sustain my effort rather than sprint like hell out of the saddle and die towards the top. They really work for me.
I like to keep my cadence up at around 90-100rpm and hate it when I have to drop below 70, so the gearing is important for me.
As for getting used to them then it took me about 20 minutes. It felt really strange at first but the really strange feeling goes away. Then after that you don't quite feel your old self - it doesn't quite feel efficient but at least the really odd sensation where you can 'feel' the odd shape of the rings has gone away. By my second ride I was really getting on with them, third ride I was loving them, and then after that I could never imagine myself going back to round rings.
For a longer climb like Mt Ventoux then I think I might just be able to keep my cadence up at around 80-90rpm in 42x29 for the steeper parts. On a climb like that you can't really grill yourself as you'll find the gear even harder later on.
If you know what sort of speeds you can pedal at for various different gradients I suggest you work out your cadence for that given speed using a gear calculator