Hi Guys, this is just my 2p worth, after flying both the 604/5 for the last 3-4 years i'd have to say it's a very capable plane that does what it says on the tin and from a passenger perspective it is superb, from a pilots point of view (my own) it really is a flying pig, its slow to react, unrewarding to hand fly and has the most bizarre attitude on approach!
You don't flare on landing as so much as check the descent! despite what Bombardier tout about their wing not being problem i have personally never felt relaxed operating in wintry conditions, all i can say is be very gentle with rotation rates and when it comes to winter ops, check, check and re-check.
As for the proline avionics, both the 4 & 21 work well although the 21 is a bit fiddly with the DCP/CCP interface, i think it works better on other aircraft (i.e Hawker) I've had no problems with either but the 605 would throw its toys out when it came to the cabin entertainment and Airshow.
Overall Its a good plane especially for the pax but it's not a plane you would ever dare take liberties with as I don't believe it would suffer fools gladly.