You should be worried if it goes more than 65C On full load.
"I only have a 400 watt corsair psu"
For your PSU you can easily run a HD5770.
To OP: don't worry your temps are great.
To shubham: No, 400W is probably not enough look here:
ATI Radeon™ HD 5770 System Requirements
* PCI Express® based PC is required with one X16 lane graphics slot available on the motherboard
* 450 Watt or greater power supply with one 75W 6-pin PCI Express® power connectors recommended (600 Watt and two 6-pin connectors for ATI CrossFireX™ technology in dual mode)
* Certified power supplies are recommended. Refer to http://ati.amd.com/certifiedPSU for a list of Certified products
* Minimum 1GB of system memory
* Installation software requires CD-ROM drive
* DVD playback requires DVD drive
* Blu-ray™ playback requires Blu-ray drive
* For an ATI CrossFireX™ system, a second ATI Radeon™ HD 5770 graphics card, an ATI CrossFireX Ready motherboard and one ATI CrossFireX Bridge Interconnect cable per graphics card (included) are required