Ever since the nee nvidia drivers came out, Mxbikes has been having serious fps issues for me. I don't believe it is beta 17 because it was working perfectly fine when it came out. My other games are working good but mxbikes took a hit and I do not know why.
Best advice I can offer is to roll back your Nvidia drivers to the previous version that was working well for you. Also, unless you are updating graphics drivers for a specific game you're better off staying with the driver set that is known to work well for your card/system. The ole adage "if it aint broke don't fix it" definitely applies to graphics drivers.
I rolled back my drivers to the last version and the game still won't run how it has before. I've tried to mess with the settings and with GeForce itself and nothing seems to work