It should last longer than you will need it to. I've never seen a card die due to overclocking. You can plug-in a $5 case fan and lay it on the back of the card to insure that it's cool enough. From what I've read, a 4400 should be able to match a 4600 or close to it. I've only tested 4600's and 4200's myself, so I can't tell you for sure what one can do. Gainward and possibly Abit should have some new 4200 cards with damn fast memory on them. I reccomend that you look for one of them. They should scream and save you a little $.
When we remember we are all mad, the mysteries disappear and life stands explained.