My friesian has a huge chunky chest and I can't find a breast girth with a martingale which fits. I have spent far too much on XL ones which end up too small, any ideas?
The Albion comes up really big - had the same problem for my large mare, but the Albion one fits. It is lovely as well. Only downside is the price - BUT for some reason, Ingatestone Saddlery do them for just 57 quid (I think it was) - almost half price to other places. They do internet and phone orders - they order them in especially. This is the one: http://www.tds-saddlers.com/ProductDetails.asp?PCLinkID=13703
I don't know how chunky Friesians are but my mare is 17.2 hh with a wide chest (it is her in my signature) and takes XL in everything including 7ft rugs - have tried other brands other than the Albion in XL and they came up too small...
You might look at the zilco endurance breastplates. My 16.1hh is in a large one, but is nowhere near the limits of the straps. Also, you can get a martingale attachment for these that just clips on.