Splitting is the best option to reduce large NSF file size into small manageable parts. If you are looking a reliable and cost effective tool, then I suggest you can try SysInfo NSF Splitter tool. The tool performs risk-free operation of splitting NSF file without making any change on the content or structure of original NSF file. The tool also support all version of Lotus Notes and Windows Operating Systems.
Know more details and download free demo version here:- http://www.nsfsecurityremover.com/nsf-split.html