I used to play risk with my friends and most often we played escalating by 1. The reason is because we found that escalating by 5 was too much, and set value was too low and is based on luck (sometimes you get too many infantry cards and are forced to cash for only 4 troops).
Escalating by 1 is fair and balances the importance of cashes with the strategy of trying to hold continents. It would only be much later in the game when the cashes might reach very high levels that the cashes would become significantly more important than holding continents. But by then players would probably be in strong positions and it would be hard for any one player to run over the entire opposition in one turn and win the game as happens in escalating.
In normal escalating games as we have them now, continents are much less important and instead it is important to eliminate players for cards, then do another cash in the same turn, and eliminate another player. I find that the strategy aspect of risk is lost to a great degree in escalating, and its all about cashing and unloading on weak players to get their cards, and repeating this process. Ive noticed in my time here that by the time the cash ins hit the range of 25-45 the games are over, usually with one run by a player who eliminates multiple opponents in the same turn with multiple cashes.
Escalating by 2 I think would also work well, though I prefer escalating by 1. Escalating by 3 I think is borderline, though I think its still a big improvement over escalating by 5 as it is now.