I'm using OVH for some years now. At the time of my decision they got the best price/value ratio. As you mentioned, with the SoYouStart offering you get dedicated servers starting from 50 EUR. I installed the proxmox Version they offered themselves. At the time of my installation that was ok for me, I had few experience with virtualization. Perhaps next time I would start with a tiny debian and do the proxmox installation myself. As "never change a running system" all is running, is still there.
My experience in all these years is quite good. Didn't felt these partioning bounderies so far. Nor did I realize bandwidth problems. BUT: my traffic is still small enough. No nationwide audience Generally: all providers are expanding. OVH now builds a new datacenter in Germany. Maybe soon, I can test traffic, when providing videos to a local audience. The machine: stable. Uptime since ever. No crash. Only once everything stood still, when I was under attac. There I appreciated very much, that i-mscp uses nginx!
Concerning installation: indeed, you have to do some postinstallation to get your networking. Their help pages were good enough, found my stuff. Today, after installation I only need few lines on the virtual console, then I'm able to continue with ssh. For the whole thing I'm writing a tutorial, but that will take some time. Have to mention, that all these things are cooperating very good with i-mscp! I only have to fix one issue, as I have to use an external DNS-Provider, who don't allows a shared Nameserver Set.
Well, nothing is perfect: I got in trouble when using these failover IPs. A good part of service, but mine had been used by spammers before so I had to clean them and wipe them out of some blacklists. But that's a general problem which has to be solved by others. IPs are recycled more and more. I'm mostly relying on IPv4, not using v6 so far. DKIM ans SPF are working well.
Hotline: had contacts via E-Mail, tickets and phone. My impression: very friendly, very customer oriented, very competent.
As of today, I would recommend them, well, at least SYS. But this was true with other providers and then changed at some point...