I'm 6'5". When I got my first road bike, I scouted 2nd hand and after about 6months, found my first roadie. It was okay for me, but as I rode more and learnt more I came to realise that the bike was only just too small for me. It was comfortable enough but not quite right. So over the course of 4 years or so, I scouted around for what I wanted in a replacement and saved the money to purchase a Felt F4 in their 61cm size.

So, I would recommend, because you already have a bike that is ok, why not give it a little going over to make it rideable and just ride it. Save your money and either keep an eye out for something second hand or even save up and buy new eventually.

Measure the top tube length of your existing bike from the centre of the steerer tube in line with where the top tube meets it and horizontally to the centre of the seat tube. Use that measurement to compare to your existing bike to gauge if any bikes on the market will fit you. Within 5mm or 1/4in will be good enough. Bike manufacturers have all different ways of measuring their sizes, but knowing the horizontal top tube measurement is a way of bringing them all down to the same level and easy for a seller to measure. If you can't find the geometry of a bike you're looking at on the net to check measurements, then ask the seller to measure for you. You can get way more technical than that, but it's a good starting point.

Have fun!