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Are you talking about this card?..How about using EVGA Precision X/XOC to set up a custom fan speed curve that limits the maximum fan RPM at a certain temperature, or use the predefined "Quiet" profile, or set a manually fixed fan speed?..I think those 650 Ti's have only a 2-wire fan (80mm) and no RPM will be reported in the software, but fan speed % should be and can be adjusted..Newegg and other places sell VGA cooling fans and stuff..Then there's always things like an el cheapo fan controller like an Evercool Twister so you could manually control the fan speed..It wouldn't be pretty, but you could also remove the existing fan (access the screws through fan opening) and strap on a more slow/quiet 80mm case fan with zip ties or rubber bands or something, cobble something together..Just a few ideas here.

The card's fan uses a mini-connector..If you want to connect a case fan to the graphics card's fan header you'd need to put another connector end on it..You could cut the mini-connector off the card's fan and use if you wanted to..A 3/4-pin case would work, just use the positive and negative wires..You could a buy Mini Fan Adapter Cable to connect a case fan to the card header too.
 
You could use a 3/4-pin motherboad fan header for a case fan, but since that mobo only has one case fan header, you'd need to wire it into the existing case fan or buy a Y-Splitter to connect two fans to the one fan header..You can buy Molex-to-Fan and SATA-to-Fan adapter cables too if the power supply has extra connectors hanging around you can use..You can search around for all those things.
 
If you want to use a fan controller for the card's fan you'd need to wire it in yourself or get something like a Mini 2-Pin GPU Fan Extension Cable.
 
You could try editing the cards VBIOS to limit the fan's maximum speed and flash it, which may not even work.
 
There's so many things you could cobble together or try..What would I do?..Hmmm..Having some experience in flashing, personally I would try that and see if it works..If not, I would buy that Evercool Twister and an extension cable somewhere for the fan, cut the wires and cobble it together..Flashing the VBIOS is not without risk and will void any warranty unless it can be flashed back..I guess the simplest (and ugliest) thing would be to remove the card's fan, cut off the mini connector and wire it to a case fan (or get an adapter) and strap it on..Many things could be done and could void any warranty, up to you though.
 
The maximum GPU temp for a 650 Ti GPU chip is 105C, but you need to keep it under 80C (I think) or it will throttle clock speed.