If I remember correctly differential = variable weighting, but I've gotten a little lazy since I snagged my own 87U English variable black.
I am still interested in English, low noise variable or all 45g 87U variety tenkeyless, but it is not currently a priority or in budget. I'd be content to wait and see if elitekeyboards got a low noise black 86U. I like having the integrated number pad, but it isn't a proper substitute for a 23UB, if you really need a number pad, which I do not. I don't need the menu key, but I do like it.
When it was looking like I'd never get an 87U, I had started digging into 91UBK-S.
http://www.smartimports.net (
They're on ebay) said they could hook me up with 91UBK-S for $325 including shipping (I'm in the US).
In the end, I decided that for the kind of money a Topre costs, I didn't want to make any compromises and I was going to get an 87U even if I had to pay a broker to get from leopold or just be happy with a tenkeyless Filco with browns.
Although, these days I would probably amend that Filco purchase with import a ducky 84% with the integrated numberpad.