My horse has been living in a pasture board for a month now and we're sticking with it! I'm sooo happy - he's feeling really good, living like a horse should live, getting more movement and better feed, there is also a shelter to hide in when the weather is bad...but guess what, the horses don't actually use it even when it's freezing cold or pouring rain - they just feel good outside! There's also a yearling filly in our herd and she is coping with it just fine, looking good and being generally healthy mentally and physically. I am now quite sure that pasture boarding is the best thing for a horse, so, if all the circumstances are suitable for your needs (access to water, non-restricted access to grass/hay, shelter, good fencing, pastures big enough for the number of the pastured horses), I'd say - go for it! Your horse will appreciate it.
I have come a long way, to surrender my shadow to the shadow of my horse.