I have a Coppertina Ninebark (Physocarpus opulifolious) which I like quite a lot. It is more like 8' x 8' and arching in form. I don't know if that will exceed your size limits too much. Nice flowers, good color in mostly sun, and I've found mine to stay healthy. P P. Summer Wine and Little Devil are perhaps redder (less gold in spring) and smaller, but I find that my Coppertina is fairly red and keeps its color beautifully all season.
{{gwi:278684}}From June 5, 2012
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Here is Coppertina just leafing out in spring. I think it was 3 or 4 years old from a one gallon pot.
{{gwi:278685}}From May 18, 2011

I'll see if I can get a photo today so you can get an idea of color after blooms. It's a bit more reddish after blooming without so many new coppery leaves and with the redder seed panicles. Fall color, which we haven't yet really started, makes the leaves redder.

Purple leafed sand cherry would be hardy enough for you and grows 8-10' tall and about 5' wide. It's a bit redder than the ninebark, but has some of the same disease issues (like black knot) that any cherry does around here. I have a fair number of wild cherry trees and so in general try to avoid growing ornamental cherries since they always look pretty miserable with spotty leaves and black knot. If you don't have many wild cherries around or yours are really healthyy, it might work for you.

I think that there are also some smallish ornamental trees with reddish leaves though larger than you indicated you want. Check out Canada Red cherry or some of the red-leafed crabapples.

Physocarpus 'Lady in Red' has stayed small for me, within your height requirements. I have several other Physocarpus and all of them have gotten enormous.

nhbabs - please can you tell me what the plant in front of the Physocarpus is in your top picture? Thanks.

Flora - it's Amsonia hubrichtii. The flowers are relatively short-lived, but it doesn't need deadheading and the feathery foliage foliage looks great all season. At about this time of year, it turns a lovely light gold, and in years like this when we haven't yet had a frost I get to enjoy the autumn color. If you have a long autumn, I'd highly recommend it. I think that it's worth growing even if you don't have late frosts, but you miss one of its best seasons.

Thanks nhbabs. Strangely, I have never seen it here, either in gardens or garden centres. Just doesn't seem to be popular. I'm not sure it would like my tiny, gloomy garden with rubbish soil. I found an article which explains it to Brits. As you can see we need educating on this plant.

Here is a link that might be useful: Amsonia