I'm looking for a new bike and am after some advice.

My current bike is about 12 years old and I've fairly recently got back into cycling. As well as being old it's in a bad state and is too small for me. It's a Univega mountain bike.

Due to a back injury I now stick to roads but need a flat handle bar. I might go on the odd very gentle path but it will be predominantly roads.

My budget is around the £400 mark, though I could go up slightly for the right bike. I've been recommended a few by different shops as follows:

Giant FCR3
Marin Larkspur
Specialized Sirrus
Giant Escape M2
Spcialized Globe Comp IG8

I know these bikes vary in type, but I'm really not sure what to go for. I want something that's going to be reasonably comfortable and as fast as possible. One salesman concerned me by saying that the FCR3 was very twitchy, and having always had mountain bikes I'm now not too sure about that.

I'm planning to do a few long journeys so need to feel comfortable cycling 100 miles a day. I also need to be able to fit panniers from time to time. Ideally I'll find something that is suited to fast road cycling but can have slightly bigger tyres fitted for the odd track. Another concern is with the FCR3 and Sirrus, as they are based on road bikes, how bumpy will they feel on poor condition roads.

If anyone has any suggestions, including other bikes, please let me know.

Thanks

Dan