Here in Michigan, in my garden:

Laguna has one main flush here, then perhaps a few blooms in the fall. I don't think of it as a repeating rose.

Quicksilver blooms steadily all summer. After the spring flush, there is always a flower or two all summer.

St. Swithun has a heavy spring flush and then a smattering of blooms as the summer goes on.

I am not in a cold zone but I would definitely say Quicksilver. I have all that you mentioned and while they are great roses none blooms as continuously as QS.

My wxperience with Laguna is the same as rosesmi.

In my garden, my small own-root band of Laguna had 3 flushes last year during its first year blooming. I find the flowers very beautiful and that's pretty good repeat in my book, but it didn't have much surviving cane after this last winter so I'm not yet sure how much of a climber it will be. However, mine is very very young so I couldn't say for certain yet. I've not grown any of the other options you mentioned, sorry.

I'm definitely looking for something that will get tall. I also have a golden celebration and princess anne to consider as well as Wollerton old hall but I think his blooms may look dirty next to white of summer memories.

The only one that I have of those that you mentioned is Quicksilver and it is a beautiful non stop bloomer. Year 3 it's about 8 feet tall.

Can't lose with Quick Silver. It's got everything a climber should have except flexible canes. They need some man handling to bend go where you want them to bend.

Moses

How tall does Quicksilver get for you Moses?

I know that Pittsburgh and Maine totally different, but since we are both zone 5/6 it may give me an idea.

Do you get substantial winter kill on your Quicksilver?

Thank you.

I got death to the ground this past winter which occurred across the board, even to Quick Silver. The brutal plunges, two weeks apart, from 50°F. to below 0F. were to blame. Most roses came back with remarkable vigor, Quick Silver among them. It should be well above average winter hardiness for you being ADR.

The longest basal cane length has been about 8'. Flower power is tremendous with abundant all season long output which for any climber is remarkable. Stiff canes, though, require a strong man approach when training.

The individual blooms last incredibly long before petal drop. QS is a an overall exceptional rose.

Scepter 'd Isle was wimpy in growth for me. No guts. Fast petal drop, smallish bloom, but blooms were lovely, and repeated very well...just a wimpy bush for me. I have no Austin's left in my garden after trialing quite a few. Have not gotten Olivia Rose, our Kristine's strong recommendation, hopefully soon.

Moses

Good for you Dirt, I planted a little guy from Northland Rosarium last summer and for first year, it has shown remarkable growth and several blooms. I can't say enough about Quicksilver. My older one has the most beautiful color blooms, so full and long lasting.

Good choice! Show us some photos later on in the season. :)

Mine is from Northland as well, Poor thing actually sat in a two gallon nursery pot for the season because I couldn't decide where I wanted to plant it.

Then I don't think it was happy because it never did much of anything, so hopefully it will be happier it's new location.