Yes and No.
Better option would be to get a spliter for the 4 pin PSU connector (not the best, but safer than using a molex to feed half of the 4/8 MB connector) - $6.00http://www.newegg.com/Product/Product.aspx?Item=N82E16812119267
It depends on how the motherboard and PSU are configured.
(1) If the molex and the 4pin ATX are on the same rail then No problem and 92) does not mater; However on multrail PSUs that is not normally the case.
(2) It is possible that all of the Positive pins are tied together on the board. You would need to verify that this is not the case (ie with a DVM measure the ohms beween the Positive pins - Put black meter lead to first red pin then with the black lead measure to the other 3 red pins, if 0 ohms they are all shorted. The problem then becomes that this will short one +12 V rail to another +12 V Rail, A No-No.
On 4 vs 8 pin atx power. 4 pin is designed for upto 125 watt CPUs, 8 pin is for > 125 Watts. The i5 is a 95 watt and will exceed that when OCed, but probably not go above the 125 Watts unless you are increasing vcore close to max. Primarily this is a factor of the IR drop accross the pins, not a limitation of the +12V rail or the wires.
Always an exception, MB may impliment seperate feed to the Regulaters (Phases) inwhich case for an OC you need to use all 8 pins. As stated you need a DVM to verify.