The safest thing would be to buy another seat that can be rearward until 12 kgs, but it's a lot of money and you mightn't get that much use out of it unless you have another child. It will also have a height limit, although this would be longer than 700 I'm sure. So really it's up to you. Many people do turn their bubs around at 8 kgs but as you know it's safer to wait. My DS is still rearward at 14 months (10kg) and will be that way for a while to come (he's in a safe n sound meridian).

You shouldn't turn him around yet as he's not quite 8 kgs, but if you keep the same seat you should probably turn him around as soon as he hits 8kgs, as it might not be safe to keep him rearward beyond the weight limit.

GL with your decision.