The highest fire glaze i have says "witness cone 5" It's an amaco sahara clear glaze. I am a bit worried about meltdown and going high with vague clay now....
Visual inspection of your ware, fired at cone 4, does not indicate that it could not fire to cone 5. You should not have any problems firing these pots to cone 5 or 6. Take your time applying your glaze, and make certain you use the correct cone. Now as to the glaze choice, your transparent glaze will do fine, but an opaque glaze will have a little more color, richness, and hide some small surface marks you may have. You may consider getting some opaque glazes.
In the future, if I may be so bold as to suggest:
1) Decide on the type of ware you wish to create-from present work I would say functional
2) Choose a clay body from a reputable distributor based on the clay fired color, working characteristics, and firing temperature you wish to fire to. Remembering that the choice of color will have an effect on the glaze colors-white bodies,brighter glazes,mid bodies, softer colors.
3) Order a box of cones for your bisque temp, and your glaze temp based on the clay and glazes you choose.
4) Set up a firing schedule sheet, notating when you start the kiln, how long you watersmoke, when you turn up the switches etc. Be specific, as this will help you become consistent in your firings. You can find recommended schedules on many different sites including clay distributors and kiln company sites.
5) Realize that it is all part of the learning curve, don't get frustrated, keep on plugging. Your pieces have merit, they just need more experience and skill development behind them to meet your expectations.