I believe bottles are designed and tested to 6 volumes. However, due to variations in bottles, and safety factors (you never want to test the limits), it is generally recommended not to exceed 3 volumes.
Every time you use a bottle you reduce it's life (only so many times you can repeatedly pressurize them; I've read 16 somewhere, but I've probably gone many more than that without any problems). When pressurizing a bottle to higher pressures (higher volumes of CO2), you use up more of it's life; the higher the pressure, the quicker you weaken it and the less the number of times you can safely re-use it.
That being said, I had a bottle blow on me about a year ago (standard 22 ozs bottle). All the rest went straight in the fridge and were consumed quickly. I checked the gravity from a couple of the bottles, and the beer FG had gone down considerably. I think I calculated 9 volumes of CO2 in the bottles, and only 1 blew.
3.5 should be OK, but no guarantees.