650w enough?!?!?!?

If it were jsut the 2x 460's I would say yes. You can take a look at the graph here:
http://www.techspot.com/review/309-geforce-gtx-460-sli-...

However adding the GTS 250 + all the other system components may push it over what the PSU is capable of, or run it really close to the max, closer than I would want to push it. I would invest is a 750 or 800w unit if you plan on keeping the 250.

A 650 watt PSU is a little light for a pair of 460s. Add on to that a GTS 250 and you're probably going to need a ~800-850W PSU.

In this power test on a overclocked I7 920 with 2x GTX460 in SLI running Furmark total system load 510watts http://www.anandtech.com/show/4061/amds-radeon-hd-6970-... It would just be enough left to allow you to have the GTS250 there as well but I would not run Furmark with it installed!