The only 110/70/17 and 130/70/17 BT45 tires that Bridgestone currently makes are the G spec tires that come as OEM on the 2004 and later GS500F models. If the dealer is trying to sell you a 130/70/17 BT45 that is not a G spec, check the date code on it first, it's probably old stock.
My 02 GS500 came with an Excedra front and a Kenda rear with about 4500 miles on the bike. Wasn't that bad a mix but I replaced them the next spring with Avon AV45/46 sport touring radials.
I put a 150/70 rear Lasertec on that bike later and ran it with an Avon AM51 front for about 800 miles till I put a Lasertec front on with it. Ran fine together and was a big improvement over the AM52 rear I removed. I wouldn't hesitate to put a Lasertec rear on with an existing Excedra front but do hesitate to suggest tire mixing to others with no idea of their riding experience or intended use of the mix. Got 10k miles from that rear Lasertec.
As far as mixing bias and radial tires goes, a radial rear with a bias front can be a good mix but a radial front with a bias rear can be a bad mix and is actually illegal in the UK. Metzeler's current suggested tire fitment for the new Bonnies is a bias Lasertec front with a Z2 radial rear.
After over 120k miles on the GSs, my current and so far favorite tires are a bias Lasertec front with a radial RoadAttack rear. Your usage and needs may vary:
http://img.photobucket.com/albums/v443/jcp8832/GS500tirelog.jpg