I'd say the software is more important than the processor, early didital recording and editing have been done one 166mhz, and standalone units rarely use anything above this. That said I use a 2ghz intel pentium laptop that's perfect and is very quick at adding effects to a track, so I doubt you'll need a i5 or i3. Sure it'll help though with the added speed of the ram but I wouldn't worry about dual core since most audio programs can't utilise them or hyperthreading. In my opinion a laptop for 500 quid or so should do you, just make sure its in or around the 2ghz mark, 3 or 4 gigs of ram and 250gb hard drive (trust me you'll need it 10 megs a minute for a raw track, say 8 tracks in a song about 4 mins long, 12-16 songs on an album and creating a backup of all of those before post production, you're talking about up to maybe 10 gigs an album and at least 25 gigs free for swap space) and invest in a decent reliable external hard drive to archive everything on. Oh and most importantly - an external sound card!!! Regardless of how good the internal one on the laptop is, it'll never be as good as an external usb/firewire soundcard and the quality can be seriously effected. I swear by MOTU
http://www.thomann.de/ie/motu_828_mk_iii.htm
But there are loads of alternative usb ones, but that's up to yourself, you can pick up a usb desk for cheap enough instead which can be quite handy
http://www.thomann.de/ie/alesis_multimix_8_usb_fx.htm
http://www.thomann.de/ie/yamaha_mg_166c_usb.htm