If you want faster speed, I'd opt for TMY400 rather than HP5. But two questions. What do you mean by long exposures? 30 seconds or so, or many minutes?
Second, are contrast filters involved? With certain of those in play, TMax 100 will have a distinct advantage over Delta 100 in terms of long exp corrections. And for most practical purposes, TMax is faster than D100 anyway due to its longer straight line. Same goes for TMY400 versus HP5.
Color? Call it dumb luck if you want to, but I just developed an 8x10 sheet of Ektar which involved a loaded filmholder which had lain around a couple years too long, and then another year after it was exposed. It was deep inside a giant hollow redwood trunk in extremely dim light, shooting at f/45. I was pretty much guessing the long exposure factor. I was pessimistic about it truning out well, but figured that I might as well use up the last of that particular box of film before it got too old. It turned out perfectly. Now that I know the gamble worked, I have a companion 8x10 shot still to develop. And I've learned something new about the film itself, which will prove useful in analogous settings.
With processing, 8X10 color film is now running around $50 a shot. I have a good reserve of it in the freezer which I bought at substantially lower price, but certainly don't want to take chances. If I had anticipated that particular set of shots in advance, I would have done a bracketing test on roll film instead.
Alas, Acros is no longer made in sheet fashion. I used up my last 4x5 sheets of it a few months ago, and the last of my 8x10 nearly a decade ago. A know a couple of people who bought up entire cases of 4x5 for personal use, 120 boxes per case (2400 sheets in all), when huge dealer discounts were involved right near the end. I paid $2.50 per roll of 120 at that time (with a single 5 pk now left). Quite a sticker shock when Acros II came out at $12.50 a roll; but I tried it anyway, and liked it even better.