enough power for tri sli?

[SupermotoMX]

well i was wondering if i could chuck in another 4870 (single) into my rig in my sig, i was wondering what kind of power it would use when coupled with the 4870x2

psu is a corsair tx650, i use 3 HDD's (one low power laptop drive and one older ide HDD) most of the time they are spun down so im going to say that when gaming there will only ever be one or the other spun up.

what do you guys think? i know it would seem like my cpu would bottleneck even the 4870x2, but surprisingly it doesnt yet

 

[SupermotoMX]

i think i am going to drop the idea on doing some more reading, having to use a 4890 with 1gb memory to get it to work. meaning i would have to upgrade psu, and most reliable review said they use 260watt max load (the 4870x2) im guessing im using 70 - 80% of the total output of my psu at max load atm?