I don't wear merino wool base layers for walking any more because although they are comfy and warm I sweat too much and they get sodden. They can take a while to reach that condition but once they do I find them cold and a little clammy. They also take a while to dry out. I'm happier with synthetics these days.
I've had two eVent jackets one by Montane and one by Rab. The Montane one wasn't durable. The Rab one I can overload after about an hour's walking.
My 66 North Neoshell jacket is doing well so far. I haven't worn it often but when I have, it's proved waterproof and windprrof and comfy. The first real test came last Saturday when I wore it all day for the first time. Fecking brilliant! I sweat a lot but this jacket remained comfortable and with little or no clammy feel. I never once felt I was in a humid atmosphere within the jacket. At the end of the day when I changed jackets I did notice some moisture inside, at the botom end of the sleeves. Durability may be an issue it's too early to tell but I tell you this I wish this fabric had been out years ago. Unless durability is a problem this fabric will be my first choice for man made fabrics from now on.
I agree with Ben. I have a Montane Fireball which is 40g/m2 and I do like it, but recent testing has indicated that after about an hour it's starting to get too warm worn with just a lightweight baselayer at 3C. I've worn it several times for half an hour after I've gotten a little chilled and it's been great.
If you're not in a hurry it can be worth going to the shops and looking at sale rails. I picked up an OR jacket down from £150 to £80 and earlier this year a Norrona Primaloft One jacket down from £250 to £150 at Snow & Rock in Covent Garden. I suppect they'll both be too warm for serious walking especially the Norrona. I'd recommend looking at Outdoor Research jackets if you can track them down. One of the best places for OR kit is in Stevenage. www.countryside.co.uk they're also a pretty good stockist of Patagonia kit.