Non Run Flats handle BETTER than Run Flats. The suspension absorbs bumps better, due to their lower unsprung weight. The vehicle will accelerate and brake (marginally) better, due to their lower rotational mass. Non-RFT's almost always have softer sidewalls than RFT's so the ride will improve. (My X5 actually rides better on my non-RFT snow tires than on my RFT summer performance tires). Plus non-RFT's cost less.
So why does your dealer lie to you? Maybe because BMW won't allow him to stock and sell non-RFT's (at the typically grossly inflated dealer prices), so he knows if you mount them he will lose the chance to bend you over when they wear out.....
EDIT: To be fair, there IS one time when RFT's will handle better than non-RFT's: Namely, when you have a flat. BFD.
2011 535xi M Sport
TiAg / Black, ZPP, ZP2, ZCV, ZCW, ZDA, 2TB, 6NR, 465, 5DL, and a Partridge in a Pear Tree
2011 X5 35D
Deep Sea Blue / Oyster, PP, SP, PSP, CWP, Tech, 20" 214's
2008 ///M3 Vert
2008 X5 3.0
2007 X5 3.0
2006 X5 3.0
2006 550iA SP
2003 540iA M-Sport
Last edited by quackbury; 12-01-2012 at 05:55 AM.