Its always a trade off ....
Some on this forum know I was part of a group on another Forum called : Need for Speed. We took the Parkjet on Hobby King (not the later smaller version) and hotted them up to see what we could get out of them. I recorded 222kph but actually had hit over 250kph but sadly recording was corrupt. It was obvious as we pushed the power / speed envelope - the motors were increasing in power drain tremendously ... The barrier seemed to be about the 140 - 150kph mark and to get past that took quite a jump in power ... To get my 222 - it took a 3800kv 450 Heli motor on a 5x5 prop sucking amps like crazy .. I had metered near 100A on ground and it allowed me just a very short run indeed ... less then 2 mins if I didn't throttle manage. I appreciate that OP is probably not looking for such extreme, but I am illustrating the exponential increase in motor against speed ... which gets worse as you push faster. Achieving 120kph is not hard at all ... and still stays in the relative manageable power bands. But higher and serious thought is needed. Balancing of battery size to motor / prop to achieve better speed / 'grunt' ... but also bearing in mind the weight increase. A little rough trick I used for a ratio of battery / motor / prop is to multiply the factors ... (assuming that prop diameter remains same) .... Motor KV x Volts x Pitch ...... a very rough but useable ratio to be guide to up / down in parts. I know purists will laugh at it - but as long as you regard it as a rough tool only - it works. You could if you wanted modify it to any factor to suit your purpose ... amps for example.
I'll fly anything if I can launch it ! Youtube : solentlifeuk