I put 700c on a 26" bike. Laced a Mavic MA to an LX hub, using same spokes as when laced to 105 hub.
Looks like I'd need to file the slot or get shorter reach brake in back to handle 27" but the long reach RX100 front brake would handle 27" no problemo.
No toe overlap at all for me.
20131016_151703[1] by
Lester Luallin, on Flickr