Both Good Boats with excellent reputations ....and I'm sure you'd be happy with either option.
Although you're not strictly comparing like with like .(I'm a big fan of Ribcraft myself...and they do hold thier money well)...but considering the choice you offer ie.
The extra size of the Osprey at 6.5m compared to a smaller 5.85m RC ...I may well be tempted to go for the Bigger option.
....That is...ALL ELSE BEING EQUAL!!
Which in the REAL world is the Rub!
.....engine choice (size and type)...hours..service history...equipment.... layout for you're needs ....and overall condition are very seldome the same when comparing used RIBS ....and would weigh heavy on my choice of these used models.
The list above and value for money would likely be my criteria for choice...The Redbay 6.5 would also be an option as would a few others.
Now if you were talking like for like....for ME the Larger Ribcraft 6.8 (the newer Osprey 6.5's are NOW named "6.8's") .....would win out every time!
Good luck with you're Hunt....incidently if you could find an extra couple of extra Grand towards you're Budget.
I think it may well bring into play alot of extra 20k+ Boats you could well be making offers on