Some questions regarding PSU

Thaisnang

Honorable
I was thinking about getting an i5 3450 & Sapphire R9 270X. Well I calculated the power needs at 95% load in this webiste --> http://www.extreme.outervision.com/psucalculatorlite.jsp
It said max 393 Watt and recommended Corsair CX 430. So I thought of getting Antec VP 450. But at 100% peak load it showed max 436 watt & recomended a 650 watt PSU. So is it possible for a system to get 100% peak load? *I'm not OC'ing* Would 450 watt be enough for my rig?