3200-asa BW film: Delta3200 vs HP5+

Greetings all;

I'm going to have to do some *very* low-light shots for something soon:
therefore in preparation I took some test rolls. Initially I thought
that Ilford Delta 3200 (which is in my opinion a 'pushed' 800-asa
emulsion) would be the way to go; however I was most pleasantly
surprised by HP5+ pushed to 3200.
I used (amongst other combinations) the following for these two:-

* Ilford Delta 3200 (exposed at 3200 -1/3rd stop), dev Microphen stock
10min at 20degsC;

* Ilford HP5+ [400] (exposed at 3200 -1/3rd stop), dev Microphen stock
17min at 20degsC.

I shot a series of 6 x 7 negs, same outdoor image, same (large) dynamic
range from shadows to highlights, same camera/lens etc etc.

The base fog on the Delta 3200 was way more than the relatively clear
HP5+ (pushed), and the resulting grain seems to be comparable.

My questions a (a) does anyone else have experience of this
comparison and (b) are there far better Delta / developer combinations
which may result in less base fog?

Thanks and my regards - F.C. Trevor Gale.