Now that youre using high resolution images, why not use a large viewing area as well? W3Schools reports that in January of 2011, 0.6% of users were still using a display resolution of 800 x 600. That means, if you want to cover all your bases, design your portfolio to fit into those dimensions. That way, users who are above 800 x 600 can still easily access your portfolio. For users on tablets and smart phones you can resize your portfolio to fit their device.
A trending topic the past couple months in the web design world is Responsive Web Design; responding to your users. Have your site adjust its layout if a user has a resolution smaller than normal. If a user has a larger screen, try making your layout adapt by loading in larger images. By using Responsive Web Design in your portfolio, you can achieve an overall greater user satisfaction. Nothing is worse than viewing a site on your iMac, only to have it fail on your iPhone the next morning on the train ride to work.