for whatever it's worth:

Just give us a percentage chance of going broke that you are willing to accept, then we can take your win rate, and give you an exact bankroll.

Now this is interesting as sites have different ways of doing HU SnG's

For example at Paradise the levels go up once every 10 hands and the average game takes 8 minutes! Once you get past 30 hands the game becomes a crapshoot.

The downside is you will struggle to get a winrate much over 60%, the plus side is just how many games you can get in in one hour's play.

Ar places like Stars the levels increase once every 10 minutes - the plus side is the huge edge this gives the better player (you can get your win % to 70% +) and the boost to poker skills generally.
The downside is that if you meet another decent player you can spend 40 minutes one one with very little profit/hour (if any).

Clearly at Stars a winning player's risk of ruin in a week (or even per 100 games) is far lower than at Dise...but Dise will help you build the bankroll quicker..(as it's better to play 3 games with a 20% edge than 1 game with a 40% one).

Generally though my suspicion is that that HU matches have some of the smallest risk of ruin of any play method provided you aren't overmatched....

No matter how good you are, I cant imagine anyone winning more than 65% or so of HU SNGS. Also, unless you are just horrible, you shouldnt lose more than 5-8 in a row.

So based on that, I would think 20 by ins is plenty. I think 50 buy ins is way to high. Not that its bad to have 50, but I thnk you can play $10's right now with $260.

Sorry for not getting back to you sooner. I liked to mix in other play just to keep my mind interested, as if I played solely HU SNGs or Ring i tend to get bored and my play deteriorates after a while.

My rule of thumb is if I have +$200 I can play $20 SNG's $100 to $200 then I play $10 SNG's. Lees then $100 I play $5 SNG's.