I am using cifs. There may be some ups and downs, depending on decryption, filesize and stuff, but in general I can pretty much use the full Gbit connection. The lowest transfer I can remember was 58 or 59 MB/s when I transfered a lot of small files.
What do you need it for? Using just HDD this server will be kinda slow. If this is just about storage, I’d recommend getting a good VPS from Hetzner, Netcup or php-friends and extend storage using a Hetzner Storage Box. 1TB for just 3,xx EUR or 5TB for around 12 EUR.
As a benefit you’ll not have to deal with failing drives and you do easy backups using snapshots.
Are you talking about dedi or vps? Lowest dedi on OVH seems to be an E3-1245 with 2TB HDD 32GB RAM for 47 EUR. Choosing SSD (240GB) adds another 12 EUR. Lowest on Hetzner - at the moment - is an E3-1275 with 64GB and 512GB NVMe for 37 EUR. Plus the Hetzner has GBit, while OVH is on 250MBit.
Have to check OVH VPS though.