You can have my 620 if you can pry it from my cold dead hands. It's unique - good backbone with a really natural splay (unlike synthetics) and ultra soft tips.I've also been pondering about the Semogue 620 or 610. And the larger 1800.
The 1800 is not really larger - it's just a but taller. It's a great brush as well once broken in, but has a bit more of a whisk broom feel. Not in a bad or derogatory way at all, but whisk broom is the best way to describe it for me.
I think the 1800 has a better feeling handle than the 620, but the 620 has a cooler looking handle. Sad that two of my favorite boars have a gaudy dye job to make them look like badgers.