..... I have the lathe going as fast as I dare when turning these type of bowls because your chisel is cutting air half the time but some would disagree
I agree with Woody, the faster the better, but be wary of any cracks or splits in the timber, and wear a full face visor.
When demonstrating this type of bowl, and turning at high speed, I very gently put my fingers agains the wood (in trailing mode) to prove that going faster IS safer, as there is less time for you fingers or tools to fall through the gap. I don't recommend that practise but it does make the point.
Another useful tip is to put a ring of masking tape round the whole piece so the corners are easier to see. I also use a piece of coloured card on top of the lathe bed to make the wood stand out better. The colour depends on the colour of wood. I often use black but white works better for some woods. In which case you might be better off using black insulation tape round the work.
It is also useful to put a piece of tape on the toolrest to mark the extremity of the wood so you know where the cuts will start/ finish.
And keep your fingers behind the toolrest!
Good luck with the bowl. I look forward to seeing the end result.