SIGPro does not use class.upload.php (which by the way is NOT outdated). It uses plain PHP GD functions. I would recommend overriding your PHP's memory_limit for SIGPro galleries only to something like 128 or 256 in SIGPro's Advanced Settings (in the component). Also, ensure thumbnail images are cached longer. You can set that to days or weeks. You'll be surpsised how much better things will perform afterwards.
Fotis / JoomlaWorks Support Team
Please search the forum before posting a new topic :)