I fear that most of negs and slides are probably not in the best condition now. Some are perfect, often those which were not filed but just thrown into boxes uncut. Those which were put in Paterson filing sheets, Kenro display sheets etc are nearly all ruined by fibres migrating, plastic stick to emulsions, PVC plasticisers affecting the film base, etc. The best preserved stuff is probably the mounted slides in boxes in filing cabinets - but that is not labelled. All my b/w negs were captioned and labelled and dated in their sheets, 30-40 years of storage hasn't really improved them and they scan very badly.
My hand has been forced too often - having to shift truckloads of stored stuff out of one place to make way for building work, storing it in another which turns out not be free from damp, never really being able to afford modern dry secure premises. The last step was when we had to have a building demolished, and on recovering the few boxes of old prints in there, discovered that some I did value (seriously) had been dumped out there in a previous clear-out and were destroyed beyond recovery.
We actually face an impossible situation - all 6,000 sq feet of the house we live in is completely full. One entire wing is full of disused office equipment and furniture, full filing cabinets, shelves and shelves of magazines. It costs me £3000 a year just in rates to keep this stuff there. I gave loads of old studio gear to a local photo society last year, but it makes no impression. I could rent a 2000 square foot factory unit and transfer all this stuff, but it earns me no money at all - it just represents what a business builds up in 30 years of operation. It would cost me £12,000 a year to store it all and for the most part, it doesn't even have a resale value.
The slides and negs could probably be stored in twenty Viking archive boxes but I already have fifty such boxes full of other items. One box contains old tape and Syquest and MagOpt drive units and all the media associated with them - none of which I can read, and all of which apart from the images belongs to some ancient version of PageMaker (etc). I spent a week earlier this year trying to recover the tapes. No luck!
My modern digital photo archives, in contrast, occupy approximately ten cubic inches for the last five years. I think they will outlive me better than the old film archives.