[EggBanjo]

Another idea I had (but it's just an idea) is only the top x% of donators get a reserved slot where x is something like 50.

I think that uncertainty in obtaining a reserved slot for donations will deter donations if the user is donating for the sole purpose of getting a reserved slot. IMHO the demand for reserved slots is exceeding the supply for a couple of the servers. Hence, it seems that those who enjoy being a regular on some of these servers (including myself) would understand if there were a set donation minimum with a defined amount of time defined for that donation. i.e. $x = y amount of time and so on.

These are the most popular servers for TF2 out there, I don't think having a defined cost model of sorts for reserved slots would deter donations or that this would be whoring out the slots. In addition you could ask for user decided donations just in general to keep the servers up without promising a reserved slot. I would suggest keeping it as simple as possible though, such as offering up only a couple of donation options for reserved slots rather than a tiered incremental type up scale of cost for increased reserved slot time etc. The current donation model for reserved slots is excessively generous. People know that. They'd pay more, or more regularly, if that's what it would take to keep a reserved slot. my 2 cents