I had a 1990 Harry Hall made from that SLX tubing - after 40 miles I felt like I'd done three rounds with Mike Tyson.
I have never ridden Columbus tubing so cant comment..........is it really that bad, my 531 was always pretty stiff, as for riding tubs, I had the exact same, GP4s with conti tubs which were glued by GP at Kendals in Casteford and on a hot day, down Mary panel hill I nearly soiled my shorts........the front wheel was true but the tub did snake on the rim, at well over 45-50mph...........if you have ever gone down Mary panel you will kow its a very quick, long hill, or was until they popped the traffic calming stuff on it.