My old boat was a Ribcraft 5.85 and now I own a Humber 6.3 Ocean Pro.
Both boats are good boats and have their pros & cons.
The Ribcraft I had, is slightly different from the current 5.85 as far as I can tell. Mine had a flat plane-ing section at the stern and with the twin engines I had, it did tend to be a bit tail heavy. As a result it slammed on landing... and it did take off a lot. It was however a very strong and dry boat and in most cases nicely finished. The 5.85 now seems to keep the V right to the stern so may well be softer than mine was.
My current Humber has a diesel o/b and is a LOT softer than my Ribcraft was and probably even dryer, (except when there's a strong beam sea.... like any boat!). The Ocean Pro isn't much wider than the Ribcraft but the main thing is the extra length of the hull. It may only be 0.45 extra overall but because Humber don't cheat by sticking a lot of tube out the back, you end up with almost an extra 0.8 mts of hull..... Hence the softer ride I feel. Certainly when I got the Humber I couldn't believe how much more hull there was – it goes on forever!!!! On the cons side, the Humber finish hasn't got the best reputation and I did have a few issues for annoying little things and one big thing – all sorted by Humber without quibble. (The Ribcraft wasn't perfect either). If you go for Humber, pay a bit extra and get them to put better quality fittings on - s/s instead of plastic etc! Having said that, they do seem to have improved things since I bought mine so I guess things are evolving.
To sum up.....
Ribcraft design is more modern - glassed in seats/consoles etc and they do have the edge on finish, (even though my console always leaked on my 5.85) but the extra length of hull and (IMHO) softer ride, swung it for me for the Humber. (Console doesn't leak either!).
You'll doubtless wish you'd bought the other which ever you buy - but they're both pretty good!
PS - You can put a wide console on the Ocean Pro so why not consider that instead of the wider Offshore?
Also, the newer, (post 2000) Humbers do seem to be keeping their price as far as I can see!