I am sure it will appreciate having more root room! That is one near hydrangea - single flowers are so big and double at that! Don't think I have ever seen even a picture of one like it. Be sure to mulch it once you get it in the ground and doubly so for winter for at least the first couple of years.
An acquaintance of mine grows hydrangeas and may be able to help you ID this one better. I am thinking you can contact her through their HYDRANGEA Album on Picasa, plus you can look though their images!
I have one pink one and it's all I can do to keep it alive and happy and occasionally blooming. I lost my Summer "Snowball Bush" and haven't even tried to replace it - don't know where I would put a new one - a Red Bud Seedling has taken it place in the small bed and I have to keep it pruned back to keep it in bounds. In effect I am trying to dwarf it and as long as I can keep it pruned back I should be able to keep it small even though it is in the ground.
Anyway, YOUR hydrangea is a pretty one! Congrats on the happy encounter!
Rebecca
Nature is trying very hard to make us succeed, but nature does not depend on us. We are not the only experiment.
- R. Buckminster Fuller