I usually send my stuff out to be printed... and yes you want 300dpi for a goodquality print.  I can't say for sure on large scale with c5, just because I'm still working on images for poster prints (I like to send out batches of ten) but I was printing some stuff through a photo place that uses fujifilm paper, (it was walmart photo) and I printed a 5x7 of two c5 images I had done back in Dec.  and they turned out wonderfully.

Christina -- "Love me but don't tell me so" Lilly Bart

My Art