I've been trying out a used set of ProAc D25's about 15 years old now. I need a speaker to stand in while i look for something more permanent after selling my Spendor D9.2's. So I'm saving up for a while and thought the D25's would be a fine stand in for a year. They are quite nice if I was honest.
But I also have some vintage ADSL910's ( late 70's early 80's vintage) that have been restored by Richard So. Well after listening to the Proac's for a couple weeks I tossed in the big ADS and if I was honest I think I'd prefer the ADS as a stand in. They have better bass more detailed, deeper, faster. probably due to being sealed and 2x10" drivers. The midrange is actually better as well more presence, detailed and better dispersion. The only places the Proac's take the big ADS is the top end, it's more extended, detailed and the imaging is better but not by as much as you'd expect. I think the dome mids and tweeters in the ADS help quite a bit here.
The Proac's are lovely specially for the used prices but sound a bit boomy or maybe its a lift in the lower mid-bass that I'm hearing, I will say though the downward port is better in my room then rear ported designs.
I'm on the fence to be honest, but there is some great vintage speakers out there you just need to restore them in most cases to get the most out of them. Also modern measurements can go a long way to bring back the sound specially if your doing a crossover rebuild already.