If i bought a tricross would it be shite with road tyres on?
Nah - it would be great.
Nope, will be pretty much as good/fast.
What about geo?
It will just handle a bit slower, it wont really be any slower due to geometry per se. It might be a little shorter than a road bike, and therefore you sit slightly more vertically, but you can play with stem length if you feel that an issue.
Gearing is more important, but I imagine it comes with a 50-34 compact chainset anyway, so same as most road bikes. the cassette might be wider-range than a normal road bike, but you wont lose out on top end gears because of it.
So.. it will be slightly slower, but not much.
What about geo?
It probaly will hold you back from a top ten in the Vuelta, but apart from that I wouldn't worry.
rob are you robj/steptoe/maxlightxc?
What cp said - absolute speed will only be marginally slower
Proper cross bikes are shorter steeper and with higher bottom brackets. Mines a hoot with road tires on for a quick (on road with slicks) commute. Proper longer rides are annoying though. To complicate matters though I think the tricross doesnt actually have cross geometry, it's slacker than road.
I ride a focus Cayo (road) and mares (cross) the cross is slightly slower but that is normally the weight penalty and massive tyres on the cross.
Equally specced frames would be pretty similar.
I find road brakes better than cantis and you should check the rims will take narrow slicks. If you are not racing a cross bike will be good for solo and club runs.
I've done centuries on my cross bike any comfort issues can probably be fixed with a new stem or similar
I suppose the easiest is to fit some cross tyres to my Ribble for trails/tow paths and then put the rd tyres back on for real rides