A link to the bad that NickNick was referring to. The SkyeHigh series also have warmer and cooler (heavier and lighter) bags for you to choose from all in 3 lengths. If you have any questions I have found the Alpkit guys excellent at answering questions and being generally helpful by email and phone.
Just an aside I ordered 3 dry bags from them last week at around 3pm, realised I had ordered the 'wrong colour' for one of them. I called them to see if they could change it, not the end of the world if they couldn't; order number and confirmation of name and postcode, what item would you like changing and to what colour? No problem. Even more impressively it was dispatched that afternoon and arrived the next day on their standard (free) first class postage. Brilliant company to deal with (just a shame about their stock issues). Have a pipedream on pre-order for when they're back in stock next month.
Thanks for putting the link up Andy3, I don't have an Alpkit sleeping bag but the things I have had from them have always been good items at a good price and their after sales service is excellent too, in my experience.
The one criticism I could level would be stock levels but that is only because something I want is out of stock. Quality Vs. price they are very good.
Alpkit are brilliant to deal with. I never have to worry something is lost in the post because it is ALWAYS there next day. (if you order before the close of business)
At your mention of 5'6" I checked the height ratings of the skyehighs (same link as above, just scroll down) and 5'6" sits right in the middle of the regular length. I suppose it depends quite how short you want the short bag to be and therefore how versatile it is?
While a short person in a long bag might not be as comfortable (warmth) as if they were in a short bag, a tall person in a short bag is likely to be more uncomfortable (position).