We use a constituent record to place anonymous donations onto Raiser's Edge. This is now very full and is very slow to open and edit. The ability to archive entries within the record and still be able to access the entries would be great. This is currently unavailable.
I hope you aren't using this record when you actually DO know who the donor is. The anonymous checkboxes on the Bio1 / Org1 and the gift records work well.
But I do know that there are situations when you don't know who the donor is - raffle ticket purchases, money collected in donation jars at events, etc. We had that at a former job of mine and experienced exactly the problem you are having. Our solution was to set up a donor anonymous record for each year. It definitely helped with the slow loading of the record, and served the purpose of "archiving" entries from previous years. The record was, of course, marked as "do not contact", "inactive", "no valid address", etc. That might be a possible solution for you.