If you mean SDEDI and single user then its capped for a single user at I believe 5Gbit peak and 6-8Gbit off-peak, don't remember exact values support gave me(had it half a year ago). Chances are they've taken on a lot more clients since then, so guessing it wasn't as stable for you as it was for me?

With tuning it is very important that you are familiar with your hardware and software setup along with expected usage. If you don't understand the full extent of the values you are changing: Stop, read official sources and learn what impact it will have. In most cases its better if you make no changes at all, this is especially true in regards to ltconfig. Only a few settings are worth changing and the rest is better done elsewhere, it's default preset(s) are not a turnkey solution. Don't recommend following system tuning guides either but most are a good starting-point on finding what is worth learning more about. A great majority are copy-pasted and either outdated, outright wrong and detrimental(especially security), or need changes based on your setup and usage.

TLDR: There's with good reason that people pay someone like Andy or others, to do tuning for them. For someone with a lack of knowledge its hard to figure which values should be changed or left default, and often end up with a shotgun-approach with some hits and a lot of misses.