Power supply possible upgrade

I'm a little concerned that my power supply may be on the limit.
My system is :
CPU: i7-920 overclocked to 3.8GHz
Motherboard: Asus P6T
RAM: OCZ DDR3 15600
GPU: MSI GTX285 dualpipe overclocked
HDD: 2 x 500GB 7200 RAID0 and 1x500GB 7200 backup
PhysX GPU: 9400GT 1Gb
Fans: 5x120mm (two on a Noctua NH-U12P)
Tuner card: Leadtek DTV2000H
Keyboard: Razer lycosa (USB)
Mouse: Microsoft Intellimouse (USB)
Scanner: Cannon N670U (USB)
OS: Vista 64bit
My current PSU is a Corsair HX620.
Why I ask is, this is a new build apart from the power supply and while playing Cryostasis the PC started to become unresponsive requiring a reboot.
While I realise that it could be other things looking at some PSU calculators online this Corsair could be on the limit.
I'm thinking maybe going up to a Enermax Revolutions85+ SLI 850W.
I might SLI my system at a latter date.
Opinions please