In the current state of the art with GPS mapping, "bike settings" are pretty meaningless. All that it will do is not route you up a motorway or other illegal road when you ask it to take you somewhere (assuming you have a capable one with maps). It's not going to avoid excessively hilly roads or anything.
As far as receiving a decent signal goes, they will all work just as well in a jersey pocket as on the handlebars.
How do you envisage using one when you do get lost?
If you just want to be located on a map, which you are then capable of navigating from, then pretty much any GPS will do (except the Edge 205/305, which don't give grid references for some reason) -- feel dubious, check the OSGR, find where you are on the map, and make appropriate decisions.
If you want to be taken home having got lost and without having to navigate from a paper map, you'll need something with reasonable built-in mapping and auto-routing, which means a more expensive GPS, plus the cost of the maps, so you are looking at an Etrex Legend (Cx, HCx or whatever), and a cost of somewhere in the range of £250-£350. To actually follow the directions when it is taking you home, you would probably want a bar mount as well, otherwise you'd constantly be rummaging in your pocket to take a look at it.
For occasional use, you could also consider a PDA with the pocket version of Memory Map, or a smartphone. Battery life may not be up to running it full time, so you'd be looking at a minute or so for satellite acquisition each time you fired the thing up. These will give you a (small) screenfull of sandard OS mapping to make use of
