It all depends what I'm doing the weather etc but for a 30-40 mile ride, I'll take anything from 300ml to 700ml, so 600ml doesn't sound like too much.
Last evening, I went for a wee recovery ride but changed my mind after 5 miles and upped the distance & pace to just under 28 mile, I used just more than 4/5 of my 500ml bottle which had half a Nuun Tablet in it. If I'm going for a more planned & sustained effort, I like to prehyrdate, sipping liquid over a period of time before I'm actually cycling. Sometimes I take just water or diluted other times I use a BR
recipe although I reduce the measures to suit an 800ml bottle and occasionally I use Nuun tablets and have also use High5 tabs and Torq powder in the past.