I use 23mm on both my road bike and my CX bike. But I've used 25mm on the CX too when I was using it purely for touring and commuting, but it's got the clearance to take massive knobblies too for CX use. Now I'm using it for winter club runs I decided to put some lighter, faster tyres on. (continental GP 4 seasons)
To be honest it really depends on what you want your bike for. I'm fortunate that I have more than one bike. My mountain bike, my carbon road bike for summer only, and my CX which is a 'do everything' bike. I need it to get me to work with all my kit, and I also need it to get me through the club runs on a Sunday. It also took me on a 600+ mile tour of Ireland earlier in the year carrying full panniers, tent, sleeping bag etc.
If you need a bike to put a rack and guards on then there's no point getting a purely racing bike. You're best looking at something that's designed for purpose - i.e. CX, touring, Audax bikes if you particularly want drop bars but rack and guard mounts too. My CX has carbon forks, the same gearing group set that you'd find on a pure road bike at that cost, and the same gearing ratios too. The only difference is I have an extra set of brakes on the bars, I have lots of clearance for larger tyres, and the bottom bracket sits slightly higher to allow for offroad clearance.
However, maybe what you're really looking for is something set up as a Winter/Workhorse bike without being an actual CX... How about
this? A guy at the club just got one and seems very happy. Pretty close to your budget too.