I've done it.
front - 100/90h18 p/n AV324.
rear - 170/80h15 p/n AV338.
http://www.motorcycleproshop.com/tires.asp
Got both delivered to my front door for $215.00 last June.
What a difference from the stock Bridgestone junk.!!
I had my dealer install them and he found a pinhole in my stock rear tube, so I had him put both tubes in new.
IMHO, you don't have to replace the tubes, but you are there so why not do it?

One caveat, some dealers get a little crinkled about installing tires that you don't buy from them. Not mine, my dealer is great. But I've heard stories... they put you on the back burner or inflate the price... just a heads up.

Again, I think the Avon Venom X's are a vast improvement over the Bridgestones.

More flags More fun!