Your requirements are pretty high in number of users, SSL Deep Inspection for blocking specific traffic inside HTTPS tunnels, QOS, VPN SSLs. So you are talking about bigger models with heavy price tag (200F and higher). I wouldn't advise you to decide based on anything (including forum posts) except the official pre-sale team from Fortinet distributor/Fortinet themselves. You want to have someone to talk to/blame if the proposed firewall does not meet the actual network needs once deployed. If you decide it yourself, it will be you.