well, I did this (and an Old Ale) yesterday and had a great time, but I doubt I'll be doing a partigyle and another batch in one day - I am beat today.
anyhow, I nailed the Barleywine - 1.104-6 actually, which was well over what I'd wanted (1.095ish) but that is okay. ~100 IBUs, it will be yummy I'm sure, just will put you under the table in one pint. Weird, b/c when I tested the first running as I was vorlaufing, I got 1.080 (just under 20 brix) which corresponds to kai's chart, but there's no way I boiled off enough in 90 minutes to get up to 1.104.
for the ESB, the second runnings tested ~1.035, so I added a 1/2lb of c-60, 1/4lb victory, 2lbs of basemalt (MO) and a lb of carapils (to counteract the 'thinness'). I miscalculated on my water addition temp, so I ended up 'mashing' for 25 min at 147, but the main mash was 154 so I expect it to be 'okay'. I ended up 1.052 which was right where I wanted to be - the wort tasted very yummy.
The one thing that really puzzled me was the amount of protein silt that I had to vorlauf out with the second runnings. Also, there was an absolute ton of cold break for the small beer. All in, I think I liked doing the big beer this way - just gotta get a better handle of efficiencies/ratio to end up on the right gravity.