Sorry, there are over 1,000 species and nearly 30,000 hybrids. Most will grow very tall when they get old, especially if they have some shade. Even with a photo of the flower, it would be hard to tell what it is.

any recommendations for a large grower?

The problem is what you mean by large grower: most of them will get large, eventually. There's a picture that cracks me up of the original 'Blewbury' (which I don't recommend regardless, it doesn't like eastern summers)...most 'Blewbury' in the US are dainty little 3-4' things. The original in HM's garden is a 10' monster!

The question you might really be asking is "any advice on a fast grower". In that case:
1) most of the so-called "ironclads" are fast. These are the large-leaf (elipidote) rhodies you are likely to find at a KY Nursery. Varities like 'English Roseum'. It's not unusual in the older suburbs of Philly to see ironclads almost reaching the roofline a 2 story colonial.
2) the rhododendron society website categorizes more uncommon varieties by height in 10 years:
http://www.rhododendron.org/alphalist.asp?Alpha=c&Genus=R&SorH=H
You would be looking for 5 or 6s.
3) buy large, to get large. Rhodyman may or may not agree w/me, but IMHO rhodies are still slow plants overall, and if grown correctly (that's the tricky part) are always going to grow very slowly their first few years. They are never like a maple or something, where the year following planting you can get a huge 3' increase in height. You shouldn't fertilize them too much...makes them more susceptible to disease. May not matter for an ironclad but even then I'd avoid pumping one with nitrogen to try to get it to grow faster. Once they are about 3'-4' tall though, and starting to form an extensive root system, they really seem to take off. If I wanted a quick rhodie garden, I'd buy large ones of that size. Of course aftercare then becomes more critical.

BTW -
if your user id means you want to garden in a so-called tropical style, I advise you seek out this:
http://www.hirsutum.info/rhododendron/hybrids/detail.php?id=20498

Very large leaves, tough as nails, and fairly fast growing. Rarefind has them but they are probably currently sold out. There may be varieties coming down the pike in a few years that will have even larger leaves, but they will not be as bulletproof as that hybrid.

thank you for all the information..I will do my best to put it to good use. I was also recommended a "rex" rhodie. they told me they will take my winters with out fail but don't like hot summers..any input on this?

thank you for all the information..I will do my best to put it to good use. I was also recommended a "rex" rhodie. they told me they will take my winters with out fail but don't like hot summers..any input on this?

The so-called large leafed rhododendron species such as rex need very specialized growing conditions. Shelter from wind is important to protect the leaves. So are cool summer tempertures and high humidity. Outside of the semi rain forest conditions of the PNW, they would be very difficult to grow unless they have a suitable micro climate. I wouldn't think winter survival would be "without fail" in Z6b, either.

Two species with larger leaves that are better bets would be r. calophytum and, especially, r. hyperythum.

There are also a few hybrids that do have big leaves and would not be as tricky to grow as straight species. 'Wyandanch Pink' is one, 'Spellbinder' - a calophytum hybrid - is another.

As davidrt noted, time is the most important element in growing any rhododendron to a large size. Rhododendron maximum plants that are more than 15 feet tall are relatively common in the mountains of NC and PA, for example, but probably represent around two generations worth of growth.